Memory cells, memory cell arrays, methods of using and methods of making

ABSTRACT

In at least one embodiment, a memory cell includes a substrate having a top surface and a first conductivity type; a first region having a second conductivity type being different from the first conductivity type, the first region being formed in the substrate and exposed at the top surface; a second region having the second conductivity type formed in the substrate, spaced apart from the first region and exposed at the top surface; a buried layer in the substrate below the first and second regions, spaced apart from the first and second regions and having the second conductivity type; a body region formed between the first and second regions and the buried layer; a gate positioned between the first and second regions and above the top surface; and a nonvolatile memory configured to store data upon transfer from the body region.

CROSS-REFERENCE

This application is a continuation of application Ser. No. 12/552,903,filed Sep. 2, 2009, which is a continuation-in-part application ofapplication Ser. No. 11/998,311, filed Nov. 29, 2007, now U.S. Pat. No.7,760,548, both of which applications and which patent are herebyincorporated herein, in their entireties, by reference thereto and towhich applications we claim priority under 35 USC §120.

Application Ser. No. 12/552,903 is a continuation-in-part application ofapplication Ser. No. 12/533,661, filed Jul. 31, 2009, now U.S. Pat. No.8,077,536, which application and which patent are hereby incorporatedherein, in their entireties, by reference thereto and to whichapplication we claim priority under 35 USC §120.

Application Ser. No. 12/552,903 is a continuation-in-part application ofapplication Ser. No. 12/545,623, filed Aug. 21, 2009, now U.S. Pat. No.8,159,868, which application and which patent are hereby incorporatedherein, in their entireties, by reference thereto and to whichapplication we claim priority under 35 USC §120.

Application Ser. No. 12/552,903 claims the benefit of U.S. ProvisionalApplication No. 61/093,726, filed Sep. 3, 2008, and U.S. ProvisionalApplication No. 61/094,540, filed Sep. 5, 2008, both of whichapplications are hereby incorporated herein, in their entireties, byreference thereto, and to which applications we claim priority under 35USC §119.

FIELD OF THE INVENTION

The present invention relates to semiconductor memory technology. Morespecifically, the present invention relates to semiconductor memoryhaving both volatile and non-volatile semiconductor memory features.

BACKGROUND OF THE INVENTION

Semiconductor memory devices are used extensively to store data. Memorydevices can be characterized according to two general types: volatileand non-volatile. Volatile memory devices such as static random accessmemory (SRAM) and dynamic random access memory (DRAM) lose data that isstored therein when power is not continuously supplied thereto.

Non-volatile memory devices, such as flash erasable programmable readonly memory (Flash EPROM) device, retain stored data even in the absenceof power supplied thereto. Unfortunately, non-volatile memory devicestypically operate more slowly than volatile memory devices. Accordingly,it would be desirable to provide a universal type memory device thatincludes the advantages of both volatile and non-volatile memorydevices, i.e., fast operation on par with volatile memories, whilehaving the ability to retain stored data when power is discontinued tothe memory device. It would further be desirable to provide such auniversal type memory device having a size that is not prohibitivelylarger than comparable volatile or non-volatile devices.

SUMMARY OF THE INVENTION

The present invention provides semiconductor memory cells, arrays ofsaid memory cells, methods of using and methods of making.

A semiconductor memory cell is provided that includes: a substratehaving a top surface, the substrate having a first conductivity typeselected from a p-type conductivity type and an n-type conductivitytype; a first region having a second conductivity type selected from thep-type and n-type conductivity types, the second conductivity type beingdifferent from the first conductivity type, the first region beingformed in the substrate and exposed at the top surface; a second regionhaving the second conductivity type, the second region being formed inthe substrate, spaced apart from the first region and exposed at the topsurface; a buried layer in the substrate below the first and secondregions, spaced apart from the first and second regions and having thesecond conductivity type; a body region formed between the first andsecond regions and the buried layer, the body region having the firstconductivity type; a gate positioned between the first and secondregions and above the top surface; and a nonvolatile memory configuredto store data upon transfer from the body region.

In at least one embodiment, the nonvolatile memory is further configuredto restore data to the body region.

In at least one embodiment, the nonvolatile memory comprises a floatinggate or trapping layer positioned in between the first and secondregions, above the top surface and below the gate.

In at least one embodiment, the nonvolatile memory comprises aresistance change element connected to one of the first and secondregions.

In at least one embodiment, the resistance change element comprises aphase change material.

In at least one embodiment, the resistance change element comprises ametal-oxide-metal system.

In at least one embodiment, nonvolatile memory is configured to storedata upon transfer from the body region resulting from an instruction toback up the data stored in the body region.

In at least one embodiment, the transfer from the body region commencesupon loss of power to the cell, wherein the cell is configured toperform a shadowing process wherein the data in the body region isloaded into and stored in the nonvolatile memory.

In at least one embodiment, the loss of power to the cell initiatingtransfer from the body region is one of unintentional power loss orintentional power loss, wherein intentional power loss is predeterminedto conserve power.

In at least one embodiment, upon restoration of power to the cell, thedata in the nonvolatile memory is loaded into the body region and storedtherein.

In at least one embodiment, the cell is configured to reset thenonvolatile memory to an initial state after loading the data into thebody region upon the restoration of power.

In at least one embodiment, the cell is configured to reset thenonvolatile memory just prior to writing new data into the nonvolatilememory during a shadowing operation.

In at least one embodiment, a semiconductor memory array is providedthat includes a plurality of the semiconductor memory cells arranged ina matrix of rows and columns.

In at least one embodiment, a plurality of the matrices are verticallystacked and electrically connected to form a three-dimensional array.

In at least one embodiment, a source line terminal is electricallyconnected to one of the first and second regions; a bit line terminal iselectrically connected to the other of the first and second regions; aword line terminal is connected to the gate; a buried well terminal iselectrically connected to the buried layer; and a substrate terminal iselectrically connected to the substrate below the buried layer.

In at least one embodiment, the nonvolatile memory comprises aresistance change element connected to one of the first and secondregions, and one of the source line terminal and the bit line terminalis connected to the resistance change element.

In at least one embodiment, a data state of the body region ismaintained by applying a voltage to the substrate terminal.

In at least one embodiment, the voltage applied to the substrateterminal automatically activates the cell when the floating body has afirst data state to refresh the first data state, and wherein when thebody region of the cell has a second data state, the cell automaticallyremains deactivated upon application of the voltage to the substrateterminal so that the body region of the cell remains in the second datastate.

In at least one embodiment, the substrate terminal is periodicallybiased by pulsing the substrate terminal with the voltage, and the datastate of the body region of the cell is refreshed upon each the pulse.

In at least one embodiment, the substrate terminal is constantly biasedby application of the voltage thereto, and the body region constantlymaintains the data state.

In at least one embodiment, the first and second regions are formed in afin that extends above the buried layer, the gate is provided onopposite sides of the fin, between the first and second regions, and thebody region is between the first and second regions and between the gateon opposite sides of the fin.

In at least one embodiment, the gate is additionally provided above atop surface of the body region.

A semiconductor memory cell is provided that includes an arrangement oflayers having alternating conductivity types selected from p-typeconductivity type and n-type conductivity type configured to function asa silicon controlled rectifier device to store data in volatile memory;and a nonvolatile memory configured to store data upon transfer fromvolatile memory.

In at least one embodiment, the silicon controlled rectifier device isprovided as a P1-N2-P3-N4 silicon-rectifier device.

In at least one embodiment, the cell includes: a substrate having a topsurface, the substrate having a p-type conductivity type; a first regionhaving an n-type conductivity type the first region being formed in thesubstrate and exposed at the top surface; a second region having then-type conductivity type, the second region being formed in thesubstrate, spaced apart from the first region and exposed at the topsurface; a buried layer in the substrate below the first and secondregions, spaced apart from the first and second regions and having then-type conductivity type; and a body region formed between the first andsecond regions and the buried layer, the body region having the p-typeconductivity type; wherein the substrate functions as the P1 region ofthe P1-N2-P3-N4 silicon-rectifier device, the buried layer functions asthe N2 region of the P1-N2-P3-N4 silicon-rectifier device, the bodyregion functions as the P3 region of the P1-N2-P3-N4 silicon-rectifierdevice and the first region or the second region functions as the N4region of the of P1-N2-P3-N4 silicon-rectifier device.

In at least one embodiment, a gate is positioned between the first andsecond regions and above the top surface.

In at least one embodiment, the nonvolatile memory comprises a floatinggate or trapping layer positioned in between the first and secondregions, above the top surface and below the gate.

In at least one embodiment, the nonvolatile memory comprises aresistance change element connected to one of the first and secondregions.

A method of operating a memory cell having a floating body for storing,reading and writing data as volatile memory, and a nonvolatile memoryfor storing data is provided, including: reading and storing data to thefloating body while power is applied to the memory cell; biasing asubstrate terminal connected to a substrate of the memory cell tooperate the memory cell as a silicon rectifier device in a conductingoperation when the floating body has a first data state, but wherein ablocking operation results when the floating body has a second datastate; and transferring the data stored in the floating body to thenonvolatile memory when power to the cell is interrupted.

A method of operating a semiconductor storage device comprising aplurality of memory cells each having a floating body for storing,reading and writing data as volatile memory, and a resistance changeelement for storing data as non-volatile memory is provided, including:reading and storing data to the floating bodies as volatile memory whilepower is applied to the device; biasing a substrate terminal connectedto a substrate of the memory cell to operate the memory cell as asilicon rectifier device in a conducting operation when the floatingbody has a first data state, but wherein a blocking operation resultswhen the floating body has a second data state; transferring the datastored in the floating bodies, by a parallel, non-algorithmic process,to the resistance change elements corresponding to the floating bodies,when power to the device is interrupted; and storing the data in theresistance change elements as non-volatile memory.

In at least one embodiment, the method further includes: transferringthe data stored in the resistance change elements, by a parallel,non-algorithmic restore process, to the floating bodies corresponding tothe resistance change elements, when power is restored to the cell; andstoring the data in the floating bodies as volatile memory.

A semiconductor memory cell formed in a vertical arrangement to providea compact cell size is provided, including: a thin capacitively coupledthyristor access device; and a resistance change memory.

In at least one embodiment, the thin capacitively coupled thyristoraccess device functions as select device and the resistance changememory functions as nonvolatile memory.

In at least one embodiment, the thin capacitively coupled thyristoraccess device comprises a stack of four layers forming p-n-p-n regions.

In at least one embodiment, the resistance change memory comprises abottom electrode, a chalcogenide material and a top electrode.

A semiconductor memory array is provided that includes a plurality ofthe semiconductor memory cells comprising a thin capacitively couplethyristor access device and a resistance change memory.

In at least one embodiment, the memory array further includes aplurality of the matrices vertically stacked and electrically connectedto form a three-dimensional array.

A method of making a semiconductor memory array is provided, including:depositing a conductor layer on an insulator layer; depositing apolysilicon layer on the conductor layer; doping the polysilicon layerto form an n-type region; patterning and etching the conductor layer andpolysilicon layer to form column lines of the array; depositing aninsulator layer on the polysilicon layer; forming holes through theinsulator layer; depositing polysilicon films to fill the holes; ionimplanting the polysilicon films to form p-n-p regions; patterning andetching the insulator layer to form row lines of the array; depositing athin insulating layer; depositing polysilicon to form a gate; depositingan additional insulating layer; depositing a bottom electrode, aresistance change material and a top electrode; patterning and etchingthe layers to form rows; and depositing an insulating layer to cap theresulting layers.

These and other features of the invention will become apparent to thosepersons skilled in the art upon reading the details of the devices andmethods as more fully described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating operation of a memory deviceaccording to the present invention.

FIG. 2 schematically illustrates an embodiment of a memory cellaccording to the present invention.

FIGS. 3A-3B illustrate various voltage states applied to terminals of amemory cell or plurality of memory cells, to carry out various functionsaccording to various embodiments of the present invention.

FIG. 4 illustrates write state “1” operations that can be carried out ona memory cell according to the present invention.

FIG. 5 illustrates a write state “0” operation that can be carried outon a memory cell according to the present invention.

FIG. 6 illustrates a holding operation that can be carried out on amemory cell according to an embodiment of the present invention.

FIGS. 7A and 7B illustrate shadowing operations according to the presentinvention.

FIGS. 8A and 8B illustrate restore operations according to the presentinvention.

FIGS. 9A-9D illustrate another embodiment of operation of a memory cellto perform volatile to non-volatile shadowing according to the presentinvention.

FIG. 9E illustrates the operation of an NPN bipolar device.

FIGS. 10A-10B illustrate another embodiment of operation of a memorycell to perform a restore process from non-volatile to volatile memoryaccording to the present invention.

FIG. 11 illustrates resetting the floating gate(s)/trapping layer(s) toa predetermined state.

FIG. 12 is a cross-sectional, schematic illustration of a memory cellaccording to an embodiment of the present invention.

FIG. 13 is a schematic, cross-sectional illustration of a memory cellaccording to an embodiment of the present invention.

FIG. 14 is a schematic illustrating an operating condition for a writestate “1” operation that can be carried out on a memory cell accordingto an embodiment of the present invention.

FIG. 15 illustrates an operating condition for a write state “0”operation that can be carried out on a memory cell according to anembodiment of the present invention.

FIGS. 16A-16B schematically illustrate shadowing operations that can becarried out on a memory cell according to an embodiment of the presentinvention.

FIGS. 17A-17B schematically illustrate restore operations that can becarried out on a memory cell according to an embodiment of the presentinvention.

FIG. 18 schematically illustrates a reset operation that can be carriedout on a memory cell according to an embodiment of the presentinvention.

FIG. 19A is a perspective, cross-sectional, schematic illustration of afin-type memory cell device according to an embodiment of the presentinvention.

FIG. 19B is a top view schematic illustration of a fin-type memory celldevice according to an embodiment of the present invention.

FIG. 20 is a cross-sectional, schematic illustration of a memory cellaccording to another embodiment of the present invention.

FIG. 21 is a cross-sectional, schematic illustration of a fin-typememory cell device according to another embodiment of the presentinvention.

FIG. 22 illustrates various states of a multi-level cell according to anembodiment of the present invention.

FIG. 23A is a schematic diagram showing an example of array architectureof a plurality of memory cells according to an embodiment of the presentinvention.

FIG. 23B is a schematic diagram showing an example of array architectureof a plurality of memory cells according to another embodiment of thepresent invention.

FIG. 24 is a flowchart illustrating operation of a memory deviceaccording to another embodiment of the present invention.

FIG. 25 is a schematic equivalent circuit model of a memory cellaccording to an embodiment of the present invention.

FIG. 26 is a cross-sectional illustration of a plurality of verticalmemory cells according to an embodiment of the present invention.

FIG. 27 is a cross-sectional illustration of a vertical stack of aplurality of the arrays of FIG. 26 to form a three-dimensional array ofmemory cells according to an embodiment of the present invention.

FIG. 28 illustrates a schematic diagram showing another example of arrayarchitecture of memory cells according to an embodiment of the presentinvention.

FIGS. 29-35 illustrate steps in a fabrication sequence of memory cellsaccording to an embodiment of the present invention

FIG. 36 is a cross-sectional illustration of a plurality of verticalmemory cells according to another embodiment of the present invention

FIG. 37 is a cross-sectional illustration of a plurality of verticalmemory cells according to another embodiment of the present invention

FIG. 38 is a cross-sectional illustration of a plurality of verticalmemory cells according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before the present devices and methods are described, it is to beunderstood that this invention is not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present invention will be limited only by the appendedclaims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassedwithin the invention. The upper and lower limits of these smaller rangesmay independently be included or excluded in the range, and each rangewhere either, neither or both limits are included in the smaller rangesis also encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned herein areincorporated herein by reference to disclose and describe the methodsand/or materials in connection with which the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “adevice” includes a plurality of such devices and reference to “thetransistor” includes reference to one or more transistors andequivalents thereof known to those skilled in the art, and so forth.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

DEFINITIONS

The terms “shadowing” “shadowing operation” and “shadowing process”refer to a process of copying the content of volatile memory tonon-volatile memory.

“Restore”, “restore operation”, or “restore process”, as used herein,refers to a process of copying the content of non-volatile memory tovolatile memory.

“Reset”, “reset operation”, or “reset process”, as used herein, refersto a process of setting non-volatile memory to a predetermined statefollowing a restore process, or when otherwise setting the non-volatilememory to an initial state (such as when powering up for the first time,prior to ever storing data in the non-volatile memory, for example).

When a terminal is referred to as being “left floating”, this means thatthe terminal is not held to any specific voltage, but is allowed tofloat to a voltage as driven by other electrical forces with the circuitthat it forms a part of.

A “resistance change material” refers to a material which resistivitycan be modified by means of electrical signals.

DESCRIPTION

FIG. 1 is a flowchart 100 illustrating operation of a memory deviceaccording to an embodiment of the present invention. At event 102, whenpower is first applied to a memory device having volatile andnon-volatile operation modes, the memory device is placed in an initialstate, in a volatile operational mode and the nonvolatile memory is setto a predetermined state. At event 104 the memory device of the presentinvention operates in the same manner as a conventional DRAM memorycell, i.e., operating as volatile memory. However, during powershutdown, or when power is inadvertently lost, or any other event thatdiscontinues or upsets power to the memory device of the presentinvention, the content of the volatile memory is loaded intonon-volatile memory at event 106, during a process which is referred tohere as “shadowing” (event 106), and the data held in volatile memory islost. Shadowing can also be performed during backup operations, whichmay be performed at regular intervals during DRAM operation 104 periods,and/or at any time that a user manually instructs a backup. During abackup operation, the content of the volatile memory is copied to thenon-volatile memory while power is maintained to the volatile memory sothat the content of the volatile memory also remains in volatile memory.Alternatively, because the volatile memory operation consumes more powerthan the non-volatile storage of the contents of the volatile memory,the device can be configured to perform the shadowing process anytimethe device has been idle for at least a predetermined period of time,thereby transferring the contents of the volatile memory intonon-volatile memory and conserving power. As one example, thepredetermined time period can be about thirty minutes, but of course,the invention is not limited to this time period, as the device could beprogrammed with virtually any predetermined time period that is longerthan the time period required to perform the shadowing process withcareful consideration of the non-volatile memory reliability.

After the content of the volatile memory has been moved during ashadowing operation to nonvolatile memory, the shutdown of the memorydevice occurs, as power is no longer supplied to the volatile memory. Atthis time, the memory device retains the stored data in the nonvolatilememory. Upon restoring power at event 108, the content of thenonvolatile memory is restored by transferring the content of thenon-volatile memory to the volatile memory in a process referred toherein as the “restore” process, after which, upon resetting the memorydevice at event 110, the memory device is again set to the initial state(event 102) and again operates in a volatile mode, like a DRAM memorydevice, event 104.

The present invention thus provides a memory device which combines thefast operation of volatile memories with the ability to retain chargethat is provided in nonvolatile memories. Further, the data transferfrom the volatile mode to the non-volatile mode and vice versa, operatein parallel by a non-algorithmic process described below, which greatlyenhances the speed of operation of the storage device. As onenon-limiting practical application of use of a memory device accordingto the present invention, a description of operation of the memorydevice in a personal computer follows. This example is in no wayintended to limit the applications in which the present invention may beused, as there are many applications, including, but not limited to:cell phones, laptop computers, desktop computers, kitchen appliances,land line phones, electronic gaming, video games, personal organizers,mp3 and other electronic forms of digital music players, and any otherapplications, too numerous to mention here, that use digital memory. Inuse, the volatile mode provides a fast access speed and is what is usedduring normal operations (i.e., when the power is on to the memorydevice). In an example of use in a personal computer (PC), when thepower to the PC is on (i.e., the PC is turned on), the memory deviceaccording to the present invention operates in volatile mode. When thePC is shut down (i.e., power is turned off), the memory content of thevolatile memory is shadowed to the non-volatile memory of the memorydevice according to the present invention. When the PC is turned onagain (power is turned on), the memory content is restored from thenon-volatile memory to the volatile memory. A reset process is thenconducted on the non-volatile memory so that its data does not interferewith the data having been transferred to the volatile memory.

FIG. 2 schematically illustrates an embodiment of a memory cell 50according to the present invention. The cell 50 includes a substrate 12of a first conductivity type, such as a p-type conductivity type, forexample. Substrate 12 is typically made of silicon, but may comprisegermanium, silicon germanium, gallium arsenide, carbon nanotubes, orother semiconductor materials known in the art. The substrate 12 has asurface 14. A first region 16 having a second conductivity type, such asn-type, for example, is provided in substrate 12 and which is exposed atsurface 14. A second region 18 having the second conductivity type isalso provided in substrate 12, which is exposed at surface 14 and whichis spaced apart from the first region 16. First and second regions 16and 18 are formed by an implantation process formed on the materialmaking up substrate 12, according to any of implantation processes knownand typically used in the art.

A buried layer 22 of the second conductivity type is also provided inthe substrate 12, buried in the substrate 12, as shown. Region 22 isalso formed by an ion implantation process on the material of substrate12. A body region 24 of the substrate 12 is bounded by surface 14, firstand second regions 16,18 and insulating layers 26 (e.g. shallow trenchisolation (STI)), which may be made of silicon oxide, for example.Insulating layers 26 insulate cell 50 from neighboring cells 50 whenmultiple cells 50 are joined to make a memory device. A floating gate ortrapping layer 60 is positioned in between the regions 16 and 18, andabove the surface 14. Trapping layer/floating gate 60 is insulated fromsurface 14 by an insulating layer 62. Insulating layer 62 may be made ofsilicon oxide and/or other dielectric materials, including high-Kdielectric materials, such as, but not limited to, tantalum peroxide,titanium oxide, zirconium oxide, hafnium oxide, and/or aluminum oxide.Floating gate/trapping layer 60 may be made of polysilicon material. Ifa trapping layer is chosen, the trapping layer may be made from siliconnitride or silicon nanocrystal, etc. Whether a floating gate 60 or atrapping layer 60 is used, the function is the same, in that they holddata in the absence of power. The primary difference between thefloating gate 60 and the trapping layer 60 is that the floating gate 60is a conductor, while the trapping layer 60 is an insulator layer. Thus,typically one or the other of trapping layer 60 and floating gate 60 areemployed in device 50, but not both.

A control gate 66 is positioned above floating gate/trapping layer 60and insulated therefrom by insulating layer 64 such that floatinggate/trapping layer 60 is positioned between insulating layer 62 andsurface 14 underlying floating gate/trapping layer 60, and insulatinglayer 64 and control gate 66 positioned above floating gate/trappinglayer 60, as shown. Control gate 66 is capacitively coupled to floatinggate/trapping layer 60. Control gate 66 is typically made of polysiliconmaterial or metal gate electrode, such as tungsten, tantalum, titaniumand their nitrides. The relationship between the floating gate/trappinglayer 60 and control gate 66 is similar to that of a nonvolatile stackedgate floating gate/trapping layer memory cell. The floatinggate/trapping layer 60 functions to store non-volatile memory data andthe control gate 66 is used for memory cell selection.

The cell 50 in FIG. 2 includes five terminals: word line (WL) terminal70, source line (SL) terminal 72, bit line (BL) terminal 74, buried well(BW) terminal 76 and substrate terminal 78. Terminal 70 is connected tocontrol gate 66. Terminal 72 is connected to first region 16 andterminal 74 is connected to second region 18. Alternatively, terminal 72can be connected to second region 18 and terminal 74 can be connected tofirst region 16. Terminal 76 is connected to buried layer 22. Substrateterminal 78 is connected to substrate 12 below buried layer 22.

When power is applied to cell 50, cell 50 operates like a currentlyavailable capacitorless DRAM cell. In a capacitorless DRAM device, thememory information (i.e., data that is stored in memory) is stored ascharge in the floating body of the transistor, i.e., in the body 24 ofcell 50. The presence of the electrical charge in the floating body 24modulates the threshold voltage of the cell 50, which determines thestate of the cell 50.

FIGS. 3A-3B illustrates relative voltages that can be applied to theterminals of memory cell 50 to perform various volatile mode operations.A read operation can be performed on memory cell 50 through thefollowing bias condition. A neutral voltage is applied to the substrateterminal 78, a neutral or positive voltage is applied to the BW terminal76, a substantially neutral voltage is applied to SL terminal 72, apositive voltage is applied to BL terminal 74, and a positive voltagemore positive than the voltage applied to BL terminal 74 is applied toWL terminal 70. If cell 50 is in a state “1” having holes in the bodyregion 24, then a lower threshold voltage (gate voltage where thetransistor is turned on) is observed compared to the threshold voltageobserved when cell 50 is in a state “0” having no holes in body region24. In one particular non-limiting embodiment, about 0.0 volts isapplied to terminal 72, about +0.4 volts is applied to terminal 74,about +1.2 volts is applied to terminal 70, about +0.6 volts is appliedto terminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the voltages applied, as described above.

Alternatively, a substantially neutral voltage is applied to thesubstrate terminal 78, a neutral or positive voltage is applied to theBW terminal 76, a substantially neutral voltage is applied to SLterminal 72, a positive voltage is applied to BL terminal 74, and apositive voltage is applied to WL terminal 70, with the voltage appliedto BL terminal 74 being more positive than the voltage applied toterminal 70. If cell 50 is in a state “1” having holes in the bodyregion 24, then the parasitic bipolar transistor formed by the SLterminal 72, floating body 24, and BL terminal 74 will be turned on anda higher cell current is observed compared to when cell 50 is in a state“0” having no holes in body region 24. In one particular non-limitingembodiment, about 0.0 volts is applied to terminal 72, about +3.0 voltsis applied to terminal 74, about +0.5 volts is applied to terminal 70,about +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the voltages applied, asdescribed above.

Alternatively, a positive voltage is applied to the substrate terminal78, a substantially neutral voltage is applied to BL terminal 74, and apositive voltage is applied to WL terminal 70. Terminals 72 and 76 areleft floating. Cell 50 provides a P1-N2-P3-N4 silicon controlledrectifier device, with substrate 78 functioning as the P1 region, buriedlayer 22 functioning as the N2 region, body region 24 functioning as theP3 region and region 16 or 18 functioning as the N4 region. Thefunctioning of the silicon controller rectifier device is described infurther detail in application Ser. No. 12/533,661 filed Jul. 31, 2009and titled “Methods of Operating Semiconductor Memory Device withFloating Body Transistor Using Silicon Controlled Rectifier Principle”.Application Ser. No. 12/533,661 is hereby incorporated herein, in itsentirety, by reference thereto. In this example, the substrate terminal78 functions as the anode and terminal 72 or terminal 74 functions asthe cathode, while body region 24 functions as a p-base to turn on theSCR device. If cell 50 is in a state “1” having holes in the body region24, the silicon controlled rectifier (SCR) device formed by thesubstrate, buried well, floating body, and the BL junction will beturned on and a higher cell current is observed compared to when cell 50is in a state “0” having no holes in body region 24. A positive voltageis applied to WL terminal 70 to select a row in the memory cell array 80(e.g., see FIGS. 23A-23B), while negative voltage is applied to WLterminal 70 for any unselected rows. The negative voltage appliedreduces the potential of floating body 24 through capacitive coupling inthe unselected rows and turns off the SCR device of each cell 50 in eachunselected row. In one particular non-limiting embodiment, about +0.8volts is applied to terminal 78, about +0.5 volts is applied to terminal70 (for the selected row), and about 0.0 volts is applied to terminal74, while terminals 72 and 76 are left floating. However, these voltagelevels may vary.

FIG. 4 illustrate a write state “1” operation that can be carried out oncell 50 according to an embodiment of the invention, by performingband-to-band tunneling hot hole injection or impact ionization hot holeinjection. To write state “1” using a band-to-band tunneling hot holeinjection mechanism, the following voltages are applied to theterminals: a positive voltage is applied to BL terminal 74, a neutralvoltage is applied to SL terminal 72, a negative voltage is applied toWL terminal 70, a positive voltage less than the positive voltageapplied to terminal 74 is applied to BW terminal 76, and a neutralvoltage is applied to the substrate terminal 78. Under these conditions,holes are injected from BL terminal 74 into the floating body region 24,leaving the body region 24 positively charged. In one particularnon-limiting embodiment, a charge of about 0.0 volts is applied toterminal 72, a voltage of about +2.0 volts is applied to terminal 74, avoltage of about −1.2 volts is applied to terminal 70, a voltage ofabout +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above.

Alternatively, to write state “1” using an impact ionization hot holeinjection mechanism, the following voltages are applied to theterminals: a positive voltage is applied to BL terminal 74, a neutralvoltage is applied to SL terminal 72, a positive voltage is applied toWL terminal 70, a positive voltage less than the positive voltageapplied to BL terminal 74 is applied to BW terminal 76, and a neutralvoltage is applied to the substrate terminal 78. Under these conditions,holes are injected from BL terminal 74 into the floating body region 24,leaving the body region 24 positively charged. In one particularnon-limiting embodiment, +0.0 volts is applied to terminal 72, a voltageof about +2.0 volts is applied to terminal 74, a charge of about +0.5volts is applied to terminal 70, a charge of about +0.6 volts is appliedto terminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above.

For example, voltage applied to terminal 72 may be in the range of about0.0 volts to about +0.4 volts, voltage applied to terminal 74 may be inthe range of about +1.5 volts to about +3.0 volts, voltage applied toterminal 70 may be in the range of about 0.0 volts to about −3.0 volts,and voltage applied to terminal 76 may be in the range of about 0.0volts to about +1.0 volts. Further, the voltages applied to terminals 72and 74 may be reversed, and still obtain the same result, e.g., apositive voltage applied to terminal 72 and a neutral charge applied toterminal 74. For example, voltage applied to terminal 72 may be in therange of about 0.0 volts to about +0.6 volts, voltage applied toterminal 74 may be in the range of about +1.5 volts to about +3.0 volts,voltage applied to terminal 70 may be in the range of about 0.0 volts toabout +1.6 volts, and voltage applied to terminal 76 may be in the rangeof about 0.0 volts to about 1.0 volts. Further, the voltages applied toterminals 72 and 74 may be reversed, and still obtain the same result,e.g., a positive voltage applied to terminal 72 and a neutral chargeapplied to terminal 74.

In an alternate write state “1” using impact ionization mechanism, apositive bias can be applied to substrate terminal 78, a positivevoltage greater than or equal to the positive voltage applied tosubstrate terminal 78 is applied to BL terminal 74, a neutral voltage isapplied to SL terminal 72, a positive voltage less than the positivevoltage applied to terminal 74 is applied to WL terminal 70, while theBW terminal 76 is left floating. The parasitic silicon controlledrectifier device of the selected cell is now turned off due to thenegative potential between the substrate terminal 78 and the BL terminal74. Under these conditions, electrons will flow near the surface of thetransistor, and generate holes through the impact ionization mechanism.The holes are subsequently injected into the floating body region 24. Inone particular non-limiting embodiment, about +0.0 volts is applied toterminal 72, a voltage of about +2.0 volts is applied to terminal 74, avoltage of about +0.5 volts is applied to terminal 70, and about +0.8volts is applied to terminal 78, while terminal 76 is left floating.However, these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above.

Alternatively, the silicon controlled rectifier device of cell 50 can beput into a state “1” (i.e., by performing a write “1” operation) byapplying the following bias: a neutral voltage is applied to BL terminal74, a positive voltage is applied to WL terminal 70, and a positivevoltage is applied to the substrate terminal 78, while SL terminal 72and BW terminal 76 are left floating. The positive voltage applied tothe WL terminal 70 will increase the potential of the floating body 24through capacitive coupling and create a feedback process that turns theSCR device on. Once the SCR device of cell 50 is in conducting mode(i.e., has been “turned on”) the SCR becomes “latched on” and thevoltage applied to WL terminal 70 can be removed without affecting the“on” state of the SCR device. In one particular non-limiting embodiment,a voltage of about 0.0 volts is applied to terminal 74, a voltage ofabout +0.5 volts is applied to terminal 70, and about +3.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the voltages applied, asdescribed above, e.g., the voltage applied to terminal 78 remainsgreater than the voltage applied to terminal 74.

A write “0” operation of the cell 50 is now described with reference toFIG. 3B and FIG. 5. To write “0” to cell 50, a negative bias is appliedto SL terminal 72, a neutral voltage is applied to BL terminal 74, aneutral or negative voltage is applied to WL terminal 70, a neutral orpositive voltage is applied to BW terminal 76 and a neutral voltage isapplied to substrate terminal 78. Under these conditions, the p-njunction (junction between 24 and 18) is forward-biased, evacuating anyholes from the floating body 24. In one particular non-limitingembodiment, about −2.0 volts is applied to terminal 72, about −1.2 voltsis applied to terminal 70, about 0.0 volts is applied to terminal 74,about +0.6 volts is applied to terminal 76 and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. Alternatively, the voltages applied to terminals 72 and74 may be switched.

Alternatively, a write “0” operation can be performed by putting thesilicon controlled rectifier device into the blocking mode. This can beperformed by applying the following bias: a positive voltage is appliedto BL terminal 74, a positive voltage is applied to WL terminal 70, anda positive voltage equal to or less positive than the positive voltageapplied to terminal 74 is applied to the substrate terminal 78, whileleaving SL terminal 72 and BW terminal 76 floating. Under theseconditions the voltage difference between anode and cathode, defined bythe voltages at substrate terminal 78 and BL terminal 74, will becometoo small to maintain the SCR device in conducting mode. As a result,the SCR device of cell 50 will be turned off. In one particularnon-limiting embodiment, a voltage of about +0.8 volts is applied toterminal 74, a voltage of about +0.5 volts is applied to terminal 70,and about +0.8 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

A holding or standby operation is described with reference to FIGS. 3Band 6. Such holding or standby operation is implemented to enhance thedata retention characteristics of the memory cells 50. The holdingoperation can be performed by applying the following bias: asubstantially neutral voltage is applied to BL terminal 74, a neutral ornegative voltage is applied to WL terminal 70, and a positive voltage isapplied to the substrate terminal 78, while leaving SL terminal 72 andBW terminal 76 floating. Under these conditions, if memory cell 50 is inmemory/data state “1” with positive voltage in floating body 24, the SCRdevice of memory cell 50 is turned on, thereby maintaining the state “1”data. Memory cells in state “0” will remain in blocking mode, since thevoltage in floating body 24 is not substantially positive and thereforefloating body 24 does not turn on the SCR device. Accordingly, currentdoes not flow through the SCR device and these cells maintain the state“0” data. In this way, an array of memory cells 50 can be refreshed byperiodically applying a positive voltage pulse through substrateterminal 78. Those memory cells 50 that are commonly connected tosubstrate terminal 78 and which have a positive voltage in body region24 will be refreshed with a “1” data state, while those memory cells 50that are commonly connected to the substrate terminal 78 and which donot have a positive voltage in body region 24 will remain in blockingmode, since their SCR device will not be turned on, and therefore memorystate “0” will be maintained in those cells. In this way, all memorycells 50 commonly connected to the substrate terminal will bemaintained/refreshed to accurately hold their data states. This processoccurs automatically, upon application of voltage to the substrateterminal 78, in a parallel, non-algorithmic, efficient process. In oneparticular non-limiting embodiment, a voltage of about 0.0 volts isapplied to terminal 74, a voltage of about −1.0 volts is applied toterminal 70, and about +0.8 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships therebetween. Alternatively, the voltage described aboveas being applied to terminal 74 may be applied to terminal 72 andterminal 74 may be left floating.

When power down is detected, e.g., when a user turns off the power tocell 50, or the power is inadvertently interrupted, or for any otherreason, power is at least temporarily discontinued to cell 50, datastored in the floating body region 24 is transferred to floatinggate/trapping layer 60. This operation is referred to as “shadowing” andis described with reference to FIGS. 7A and 7B. To perform the shadowingoperation, both SL terminal 72 and BL terminal 74 are left floating(i.e., not held to any specific voltage, but allowed to float to theirrespective voltages). A high positive voltage (e.g., about +18 volts) isapplied to WL terminal 70, a low positive voltage (e.g., about +0.6volts) is applied to BW terminal 76, and the substrate terminal 78 isgrounded. If cell 50 is in a state “1” as illustrated in FIG. 7A, thushaving holes in body region 24, a lower electric field between thefloating gate/trapping layer 60 and the floating body region 24 isobserved in comparison to the electric field observed between thefloating gate/trapping layer 60 and the floating body region 24 whencell 50 is in a state “0” as illustrated in FIG. 7B.

The high electric field between the floating gate/trapping layer region60 and the floating body region 24, when floating body 24 is at state“0” causes electrons to tunnel from floating body 24 to floatinggate/trapping layer 60 and the floating gate/trapping layer 60 thusbecomes negatively charged. Conversely, the relatively lower electricfield existent between the floating gate/trapping layer region 60 andfloating body 24 when cell 50 is in the state “1” is not sufficient tocause electron tunneling from the floating body 24 to floatinggate/trapping layer 60 and therefore floating gate/trapping layer 60does not become negatively charged in this situation.

In one particular non-limiting embodiment, terminals 72 and 74 areallowed to float, about +18 volts is applied to terminal 70, about +0.6volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78. However, these voltage levels may vary, while maintainingthe relative relationships between the charges applied, as describedabove. For example, voltage applied to terminal 70 may be in the rangeof about +12.0 volts to about +20.0 volts, and voltage applied toterminal 76 may be in the range of about 0.0 volts to about 1.0 volts.

When power is restored to cell 50, the state of the cell 50 as stored onfloating gate/trapping layer 60 is restored into floating body region24. The restore operation (data restoration from non-volatile memory tovolatile memory) is described with reference to FIGS. 8A and 8B. Priorto the restore operation/process, the floating body 24 is set to apositive charge, i.e., a “1” state is written to floating body 24. Inone embodiment, to perform the restore operation, both SL terminal 72and BL terminal 74 are left floating. A large negative voltage isapplied to WL terminal 70 and a low positive voltage is applied to BWterminal 76, while substrate terminal 78 is grounded. If the floatinggate/trapping layer 60 is not negatively charged, no electrons willtunnel from floating gate/trapping layer 60 to floating body 24, andcell 50 will therefore be in a state “1”. Conversely, if floatinggate/trapping layer 60 is negatively charged, electrons tunnel fromfloating gate/trapping layer 60 into floating body 24, thereby placingcell 50 in a state “0”. In one particular non-limiting embodiment, about−18.0 volts is applied to terminal 70, and about +0.6 volts is appliedto terminal 76. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. For example, voltage applied to terminal 70 may be inthe range of about −12.0 volts to about −20.0 volts, and voltage appliedto terminal 76 may be in the range of about 0.0 volts to about +1.0volts, while about 0.0 volts is applied to terminal 78.

Note that this process occurs non-algorithmically, as the state of thefloating gate/trapping layer 60 does not have to be read, interpreted,or otherwise measured to determine what state to restore the floatingbody 24 to. Rather, the restoration process occurs automatically, drivenby electrical potential differences. Accordingly, this process is ordersof magnitude faster than one that requires algorithmic intervention.Similarly, it is noted that the shadowing process also is performed as anon-algorithmic process. From these operations, it has been shown thatcell 50 provides a memory cell having the advantages of a DRAM cell, butwhere non-volatility is also achieved.

FIGS. 9A-9D illustrate another embodiment of operation of cell 50 toperform a volatile to non-volatile shadowing process, which operates bya hot electron injection process, in contrast to the tunneling process(e.g., Fowler-Nordheim tunneling process) described above with regard toFIGS. 7A-7B. FIG. 9E illustrates the operation of an NPN bipolar device90, as it relates to the operation of cell 50. Floating body 24 isrepresented by the terminal to which voltage V_(FB) is applied in FIG.9E, and the terminals 72 and 74 are represented by terminals to whichvoltages V_(SL) and V_(BL) are applied, respectively. When V_(FB) is apositive voltage, this turns on the bipolar device 90, and when V_(FB)is a negative or neutral voltage, the device 90 is turned off. Likewise,when floating body 24 has a positive voltage, this turns on the cell 50so that current flows through the NPN junction formed by 16, 24 and 18in the direction indicated by the arrow in floating body 24 in FIG. 9A,and when floating body 24 has a negative or neutral voltage, cell isturned off, so that there is no current flow through the NPN junction.

To perform a shadowing process according to the embodiment describedwith regard to FIGS. 9A-9D, a high positive voltage is applied toterminal 72 and a substantially neutral voltage is applied to terminal74. Alternatively, a high positive voltage can be applied to terminal 74and a substantially neutral voltage can be applied to terminal 72. Apositive voltage less than the positive voltage applied to terminal 72or 74 is applied to terminal 70 and a low positive voltage less than thepositive voltage applied to terminal 72 or 74 is applied to terminal 76.A high voltage in this case is a voltage greater than or equal to about+3 volts. In one example, a voltage in the range of about +3 to about +6volts is applied, although it is possible to apply a higher voltage. Thefloating gate/trapping layer 60 will have been previously initialized orreset to have a positive charge prior to the operation of the cell 50 tostore data in non-volatile memory via floating body 24. When floatingbody 24 has a positive charge/voltage, the NPN junction is on, as notedabove, and electrons flow in the direction of the arrow shown in thefloating body 24 in FIG. 9A. The application of the high voltage toterminal 72 at 16 energizes/accelerates electrons traveling through thefloating body 24 to a sufficient extent that they can “jump over” theoxide barrier between floating body 24 and floating gate/trapping layer60, so that electrons enter floating gate/trapping layer 60 as indicatedby the arrow into floating gate/trapping layer 60 in FIG. 9A.Accordingly, floating gate/trapping layer 60 becomes negatively chargedby the shadowing process, when the volatile memory of cell 50 is instate “1” (i.e., floating body 24 is positively charged), as shown inFIG. 9B.

When volatile memory of cell 50 is in state “0”, i.e., floating body 24has a negative or neutral charge/voltage, the NPN junction is off, asnoted above, and electrons do not flow in the floating body 24, asillustrated in FIG. 9C. Accordingly, when voltages are applied to theterminals as described above, in order to perform the shadowing process,the high positive voltage applied to terminal 72 does not cause anacceleration of electrons in order to cause hot electron injection intofloating gate/trapping layer 60, since the electrons are not flowing.Accordingly, floating gate/trapping layer 60 retains its positive chargeat the end of the shadowing process, when the volatile memory of cell 50is in state “0” (i.e., floating body 24 is neutral or negativelycharged), as shown in FIG. 9D. Note that the charge state of thefloating gate/trapping layer 60 is complementary to the charge state ofthe floating body 24 after completion of the shadowing process. Thus, ifthe floating body 24 of the memory cell 50 has a positive charge involatile memory, the floating gate/trapping layer 60 will becomenegatively charged by the shadowing process, whereas if the floatingbody of the memory cell 50 has a negative or neutral charge in volatilememory, the floating gate/trapping layer 60 will be positively chargedat the end of the shadowing operation. The charges/states of thefloating gates/trapping layers 60 are determined non-algorithmically bythe states of the floating bodies, and shadowing of multiple cellsoccurs in parallel, therefore the shadowing process is very fast.

In one particular non-limiting example of the shadowing processaccording to this embodiment, about +3 volts are applied to terminal 72,about 0 volts are applied to terminal 74, about +1.2 volts are appliedto terminal 70, about +0.6 volts are applied to terminal 76, and about0.0 volts is applied to terminal 78. However, these voltage levels mayvary, while maintaining the relative relationships between the chargesapplied, as described above. For example, voltage applied to terminal 72may be in the range of about +3 volts to about +6 volts, the voltageapplied to terminal 74 may be in the range of about 0.0 volts to about+0.4 volts, the voltage applied to terminal 70 may be in the range ofabout 0.0 volts to about +1.6 volts, and voltage applied to terminal 76may be in the range of about 0.0 volts to about +1.0 volts, while about0.0 volts is applied to terminal 78.

Turning now to FIGS. 10A-10B, another embodiment of operation of cell 50to perform a restore process from non-volatile to volatile memory isschematically illustrated, in which the restore process operates by aband-to-band tunneling hot hole injection process (modulated by thefloating gate/trapping layer 60 charge), in contrast to the electrontunneling process described above with regard to FIGS. 8A-8B. In theembodiment illustrated in FIGS. 10A-10B, the floating body 24 is set toa neutral or negative charge prior to performing the restoreoperation/process, i.e., a “0” state is written to floating body 24. Inthe embodiment of FIGS. 10A-10B, to perform the restore operation,terminal 72 is set to a substantially neutral voltage, a positivevoltage is applied to terminal 74, a negative voltage is applied toterminal 70, a positive voltage that is less positive than the positivevoltage applied to terminal 74 is applied to terminal 76, and asubstantially neutral voltage is applied to terminal 78. If the floatinggate/trapping layer 60 is negatively charged, as illustrated in FIG.10A, this negative charge enhances the driving force for theband-to-band hot hole injection process, whereby holes are injected fromthe n-region 18 into floating body 24, thereby restoring the “1” statethat the volatile memory cell 50 had held prior to the performance ofthe shadowing operation. If the floating gate/trapping layer 60 is notnegatively charged, such as when the floating gate/trapping layer 60 ispositively charged as shown in FIG. 10B or is neutral, the hotband-to-band hole injection process will not occur, as illustrated inFIG. 10B, resulting in memory cell 50 having a “0” state, just as it didprior to performance of the shadowing process. Accordingly, if floatinggate/trapping layer 60 has a positive charge after shadowing isperformed, the volatile memory of floating body 24 will be restored tohave a negative charge (“0” state), but if the floating gate/trappinglayer 60 has a negative or neutral charge, the volatile memory offloating body 24 will be restored to have a positive charge (“1” state).

In one particular non-limiting example of this embodiment, about 0 voltsis applied to terminal 72, about +2 volts is applied to terminal 74,about −1.2 volts is applied to terminal 70, about +0.6 volts is appliedto terminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above. Forexample, voltage applied to terminal 72 may be in the range of about+1.5 volts to about +3.0 volts, voltage applied to terminal 74 may be inthe range of about 0.0 volts to about +0.6 volts, voltage applied toterminal 70 may be in the range of about 0.0 volts to about −3.0 volts,voltage applied to terminal 76 may be in the range of about 0.0 volts toabout +1.0 volts, and about 0.0 volts is applied to terminal 78.

Note that this process occurs non-algorithmically, as the state of thefloating gate/trapping layer 60 does not have to be read, interpreted,or otherwise measured to determine what state to restore the floatingbody 24 to. Rather, the restoration process occurs automatically, drivenby electrical potential differences. Accordingly, this process is ordersof magnitude faster than one that requires algorithmic intervention.From these operations, it has been shown that cell 50 provides a memorycell having the advantages of a DRAM cell, but where non-volatility isalso achieved.

After restoring the memory cell(s) 50, the floating gate(s)/trappinglayer(s) 60 is/are reset to a predetermined state, e.g., a positivestate, so that each floating gate/trapping layer 60 has a known stateprior to performing another shadowing operation. The reset processoperates by the mechanism of electron tunneling from the floatinggate/trapping layer 60 to the source region 16, as illustrated in FIG.11.

To perform a reset operation according to the embodiment of FIG. 11, ahighly negative voltage is applied to terminal 70, a substantiallyneutral voltage is applied to SL terminal 72, BL terminal 74 is allowedto float or is grounded, a positive voltage is applied to terminal 76,while substrate terminal 78 is grounded. By applying a neutral voltageto terminal 72 and maintaining the voltage of region 16 to besubstantially neutral, this causes region 16 to function as a sink forthe electrons from floating gate/trapping layer 60 to travel to byelectron tunneling. A large negative voltage is applied to WL terminal70 and a low positive voltage is applied to BW terminal 76. If thefloating gate/trapping layer 60 is negatively charged, electrons willtunnel from floating gate/trapping layer 60 to region 16, and floatinggate/trapping layer 60 will therefore become positively charged. As aresult of the reset operation, all of the floating gate/trapping layerswill become positively charged. In one particular non-limitingembodiment, about −18.0 volts is applied to terminal 70, about +0.6volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78. However, these voltage levels may vary, while maintainingthe relative relationships between the charges applied, as describedabove. For example, voltage applied to terminal 70 may be in the rangeof about −12.0 volts to about −20.0 volts, the voltage applied toterminal 76 may be in the range of about 0.0 volts to about 1.0 volts,and about 0.0 volts is applied to terminal 78.

Having described the various operations of cell 50 above, reference isagain made to FIG. 1 to describe operation of a memory device having aplurality of memory cells 50. The number of memory cells can varywidely, for example ranging from less than 100 Mb to several Gb, ormore. It is noted that, except for the DRAM operations of writing andreading (event 104), which by necessity must be capable of individual,controlled operations, the remaining operations shown in FIG. 1 can allbe carried out as parallel, non-algorithmic operations, which results ina very fast operating memory device.

At event 102, the memory device is initialized by first setting all ofthe floating gates/trapping layers to a positive state, in a manner asdescribed above with reference to FIG. 11, for example. For example, acontrol line can be used to input a highly negative voltage to each ofterminals 70, in parallel, with voltage settings at the other terminalsas described above with reference to FIG. 11. Individual bits (ormultiple bits, as described below) of data can be read from or writtento floating bodies 24 of the respective cells at event 104.

The shadowing operation at event 106 is conducted in a mass parallel,non-algorithmic process, in any of the same manners described above,with each of the cells 50 performing the shadowing operationsimultaneously, in a parallel operation. Because no algorithmicinterpretation or measurement is required to transfer the data fromnon-volatile to volatile memory (24 to 60), the shadowing operation isvery fast and efficient.

To restore the data into the volatile portion of the memory cells 50 ofthe memory device (i.e., restore charges in floating bodies 24), a state“0” is first written into each of the floating bodies 24, by a parallelprocess, and then each of the floating bodies is restored in any of thesame manners described above with regard to a restoration process of asingle floating body 24. This process is also a mass, parallelnon-algorithmic process, so that no algorithmic processing ormeasurement of the states of the floating gates/trapping layers 60 isrequired prior to transferring the data stored by the floatinggates/trapping layers 60 to the floating bodies 24. Thus, the floatingbodies are restored simultaneously, in parallel, in a very fast andefficient process.

Upon restoring the volatile memory at event 108, the floatinggates/trapping layers 60 are then reset at event 110, to establish apositive charge in each of the floating gates/trapping layers, in thesame manner as described above with regard to initializing at event 110.

FIG. 12 shows another embodiment of a memory cell 50 according to thepresent invention. The cell 50 includes a substrate 12 of a firstconductivity type, such as a p-type conductivity type, for example.Substrate 12 is typically made of silicon, but may comprise germanium,silicon germanium, gallium arsenide, carbon nanotubes, or othersemiconductor materials known in the art. The substrate 12 has a surface14. A first region 16 having a second conductivity type, such as n-type,for example, is provided in substrate 12 and which is exposed at surface14. A second region 18 having the second conductivity type is alsoprovided in substrate 12, which is exposed at surface 14 and which isspaced apart from the first region 16. First and second regions 16 and18 are formed by an implantation process formed on the material makingup substrate 12, according to any of implantation processes known andtypically used in the art.

A buried layer 22 of the second conductivity type is also provided inthe substrate 12, buried in the substrate 12, as shown. Region 22 isalso formed by an ion implantation process on the material of substrate12. A body region 24 of the substrate 12 is bounded by surface 14, firstand second regions 16,18 and insulating layers 26 (e.g. shallow trenchisolation (STI, which may be made of silicon oxide, for example).Insulating layers 26 insulate cell 50 from neighboring cells 50 whenmultiple cells 50 are joined to make a memory device. A gate 60 ispositioned in between the regions 16 and 18, and above the surface 14.The gate 60 is insulated from surface 14 by an insulating layer 62.Insulating layer 62 may be made of silicon oxide and/or other dielectricmaterials, including high-K dielectric materials, such as, but notlimited to, tantalum peroxide, titanium oxide, zirconium oxide, hafniumoxide, and/or aluminum oxide. The gate 60 may be made of polysiliconmaterial or metal gate electrode, such as tungsten, tantalum, titaniumand their nitrides.

A resistance change memory element 40 is positioned above one of theregions 16, 18 (18 in FIG. 12) having second conductivity type andconnected to one of the terminals 72, 74 (74 in FIG. 12). The resistancechange memory element 40 is shown as a variable resistor, and may beformed from phase change memory material such as a chalcogenide orconductive bridging memory or metal oxide memory, and may take the formof metal-insulator-metal structure, in which transition metal oxide orperovskite metal oxide is used in conjunction with any reasonably goodconductors.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, bit line (BL) terminal 74, buried well (BW)terminal 76 and substrate terminal 78. Terminal 70 is connected to thegate 60. Terminal 74 is connected to first region 16 and terminal 72 isconnected to resistance change memory element 40 which is, in turn,connected to second region 18. Alternatively, terminal 72 can beconnected to resistance change memory element 40 and terminal 74 can beconnected to first region 16. Terminal 76 is connected to buried layer22 and terminal 78 is connected to substrate 12.

A non-limiting embodiment of the memory cell 50 is shown in FIG. 13. Thesecond conductivity region 16 is connected to an address line terminal74 through a conductive element 38. The resistance change memory element40 in this embodiment includes a bottom electrode 44, a resistancechange material 46 and a top electrode 48. Resistance change memoryelement 40 is connected to the second conductivity region 18 on thesubstrate 12 through a conductive element 42. The resistance changematerial 46 may be connected to an address line (such as terminal 72 inFIG. 13) through electrode 48 formed from a conductive material. Theconductive element 42 may comprise tungsten or silicided siliconmaterials. Electrodes 44, 48 may be formed from one or more conductivematerials, including, but not limited to titanium nitride, titaniumaluminum nitride, or titanium silicon nitride. Resistance changematerial 46 is a material in which properties, such as electricalresistance, can be modified using electrical signals. For the case ofphase change memory elements, the resistivity depends on the crystallinephase of the material, while for the metal oxide materials, theresistivity typically depends on the presence or absence of conductivefilaments. A crystalline phase of a phase change type resistive changematerial exhibits a low resistivity (e.g., ˜1 kΩ) state and an amorphousphase of that material exhibits a high resistivity state (e.g., >100kΩ). Examples of phase change material include alloys containingelements from Column VI of the periodic table, such as GeSbTe alloys.Examples of metal-insulator-metal resistance change materials include avariety of oxides such as Nb₂O₅, Al₂O₃, Ta₂O₅, TiO₂, and NiO andperovskite metal oxides, such as SrZrO₃, (Pr,Ca)MnO₃ and SrTiO₃:Cr.

When power is applied to cell 50, cell 50 operates like a capacitorlessDRAM cell. In a capacitorless DRAM device, the memory information (i.e.,data that is stored in memory) is stored as charge in the floating bodyof the transistor, i.e., in the bodies 24 of the cells 50 of a memorydevice. The presence of the electrical charge in the floating body 24modulates the threshold voltage of the cell 50, which determines thestate of the cell 50. In one embodiment, the non-volatile memory 40 isinitialized to have a low resistance state.

A read operation can be performed on memory cell 50 through thefollowing bias condition. A neutral voltage is applied to the substrateterminal 78, a neutral or positive voltage is applied to the BW terminal76, a substantially neutral voltage is applied to SL terminal 72, apositive voltage is applied to BL terminal 74, and a positive voltagemore positive than the voltage applied to BL terminal 74 is applied toWL terminal 70. If cell 50 is in a state “1” having holes in the bodyregion 24, then a lower threshold voltage (gate voltage where thetransistor is turned on) is observed compared to the threshold voltageobserved when cell 50 is in a state “0” having no holes in body region24. In one particular non-limiting embodiment, about 0.0 volts isapplied to terminal 72, about +0.4 volts is applied to terminal 74,about +1.2 volts is applied to terminal 70, about +0.6 volts is appliedto terminal 76, and about 0.0 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the voltages applied, as described above.

Alternatively, a substantially neutral voltage is applied to thesubstrate terminal 78, a neutral or positive voltage is applied to theBW terminal 76, a substantially neutral voltage is applied to SLterminal 72, a positive voltage is applied to BL terminal 74, and apositive voltage is applied to WL terminal 70, with the voltage appliedto BL terminal 74 being more positive than the voltage applied toterminal 70. If cell 50 is in a state “1” having holes in the bodyregion 24, then the parasitic bipolar transistor formed by the SLterminal 72, floating body 24, and BL terminal 74 will be turned on anda higher cell current is observed compared to when cell 50 is in a state“0” having no holes in body region 24. In one particular non-limitingembodiment, about 0.0 volts is applied to terminal 72, about +3.0 voltsis applied to terminal 74, about +0.5 volts is applied to terminal 70,about +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the voltages applied, asdescribed above.

Alternatively, a positive voltage is applied to the substrate terminal78, a substantially neutral voltage is applied to BL terminal 74, and apositive voltage is applied to WL terminal 70. Cell 50 provides aP1-N2-P3-N4 silicon controlled rectifier device, with substrate 78functioning as the P1 region, buried layer 22 functioning as the N2region, body region 24 functioning as the P3 region and region 16 or 18functioning as the N4 region. The functioning of the silicon controllerrectifier device is described in further detail in application Ser. No.12/533,661 filed Jul. 31, 2009 and titled “Methods of OperatingSemiconductor Memory Device with Floating Body Transistor Using SiliconControlled Rectifier Principle”. In this example, the substrate terminal78 functions as the anode and terminal 72 or terminal 74 functions asthe cathode, while body region 24 functions as a p-base to turn on theSCR device. If cell 50 is in a state “1” having holes in the body region24, the silicon controlled rectifier (SCR) device formed by thesubstrate, buried well, floating body, and the BL junction will beturned on and a higher cell current is observed compared to when cell 50is in a state “0” having no holes in body region 24. A positive voltageis applied to WL terminal 70 to select a row in the memory cell array 80(e.g., see FIGS. 23A-B), while negative voltage is applied to WLterminal 70 for any unselected rows. The negative voltage appliedreduces the potential of floating body 24 through capacitive coupling inthe unselected rows and turns off the SCR device of each cell 50 in eachunselected row. In one particular non-limiting embodiment, about +0.8volts is applied to terminal 78, about +0.5 volts is applied to terminal70 (for the selected row), and about 0.0 volts is applied to terminal74. However, these voltage levels may vary.

FIG. 14 illustrates write state “1” operations that can be carried outon cell 50, by performing band-to-band tunneling hot hole injection orimpact ionization hot hole injection. To write state “1” usingband-to-band tunneling mechanism, the following voltages are applied tothe terminals: a positive voltage is applied to BL terminal 74, asubstantially neutral voltage is applied to SL terminal 72, a negativevoltage is applied to WL terminal 70, a positive voltage less than thepositive voltage applied to terminal 74 is applied to BW terminal 76,and a substantially neutral voltage is applied to the substrate terminal78. Under these conditions, holes are injected from BL terminal 74 intothe floating body region 24, leaving the body region 24 positivelycharged. In one particular non-limiting embodiment, a charge of about0.0 volts is applied to terminal 72, a charge of about +2.0 volts isapplied to terminal 74, a charge of about −1.2 volts is applied toterminal 70, a charge of about +0.6 volts is applied to terminal 76, andabout 0.0 volts is applied to terminal 78. However, these voltage levelsmay vary, while maintaining the relative relationships between thevoltages applied, as described above.

Alternatively, to write state “1” using an impact ionization mechanism,the following voltages can be applied to the terminals: a positivevoltage is applied to BL terminal 74, a substantially neutral voltage isapplied to SL terminal 72, a positive voltage less than the positivevoltage applied to terminal 74 is applied to WL terminal 70, a positivevoltage less positive than the positive voltage applied to BL terminal74 is applied to BW terminal 76, and a substantially neutral voltage isapplied to the substrate terminal 78. Under these conditions, holes areinjected from BL terminal 74 into the floating body region 24, leavingthe body region 24 positively charged. In one particular non-limitingembodiment, +0.0 volts is applied to terminal 72, a charge of about +2.0volts is applied to terminal 74, a charge of about +0.5 volts is appliedto terminal 70, a charge of about +0.6 volts is applied to terminal 76,and about 0.0 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe voltages applied, as described above.

In an alternate write state “1” using impact ionization mechanism, apositive bias can be applied to substrate terminal 78. The parasiticsilicon controlled rectifier device of the selected cell is now turnedoff due to the negative potential between the substrate terminal 78 andthe BL terminal 74. The functioning of the silicon controller rectifierdevice is described in further detail in application Ser. No. 12/533,661filed Jul. 31, 2009 and titled “Methods of Operating SemiconductorMemory Device with Floating Body Transistor Using Silicon ControlledRectifier Principle”. Under these conditions, electrons will flow nearthe surface of the transistor, and generate holes through impactionization mechanism. The holes are subsequently injected into thefloating body region 24. In one particular non-limiting embodiment, +0.0volts is applied to terminal 72, a charge of about +2.0 volts is appliedto terminal 74, a charge of about +0.5 volts is applied to terminal 70,and about +0.8 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe voltages applied, as described above.

Alternatively, the silicon controlled rectifier device of cell 50 can beput into a state “1” (i.e., by performing a write “1” operation) byapplying the following bias: a neutral voltage is applied to BL terminal74, a positive voltage is applied to WL terminal 70, and a positivevoltage is applied to the substrate terminal 78, while SL terminal 72and BW terminal 76 are left floating. The positive voltage applied tothe WL terminal 70 will increase the potential of the floating body 24through capacitive coupling and create a feedback process that turns theSCR device on. Once the SCR device of cell 50 is in conducting mode(i.e., has been “turned on”) the SCR becomes “latched on” and thevoltage applied to WL terminal 70 can be removed without affecting the“on” state of the SCR device. In one particular non-limiting embodiment,a voltage of about 0.0 volts is applied to terminal 74, a voltage ofabout +0.5 volts is applied to terminal 70, and about +3.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the voltages applied, asdescribed above, e.g., the voltage applied to terminal 78 remainsgreater than the voltage applied to terminal 74.

A write “0” operation of the cell 50 is now described with reference toFIG. 15. To write “0” to cell 50, a negative bias is applied to SLterminal 72 and/or BL terminal 74, a neutral or negative voltage isapplied to WL terminal 70, and a substantially neutral voltage isapplied to substrate terminal 78. Under these conditions, the p-njunction (junction between 24 and 16 and between 24 and 18) isforward-biased, evacuating any holes from the floating body 24. In oneparticular non-limiting embodiment, about −1.0 volts is applied toterminal 72, about −1.0 volts is applied to terminal 70, and about 0.0volts is applied to terminal 78. However, these voltage levels may vary,while maintaining the relative relationships between the voltagesapplied, as described above.

Alternatively, a write “0” operation can be performed to cell 50 byapplying a positive bias to WL terminal 70, and substantially neutralvoltages to SL terminal 72, BL terminal 74, and substrate terminal 78.Under these conditions, the holes will be evacuated from the floatingbody 24. In one particular non-limiting embodiment, about 1.0 volts isapplied to terminal 70, about 0.0 volts are applied to terminals 72 and74, and about 0.0 volts is applied to terminal 78. However, thesevoltage levels may vary, while maintaining the relative relationshipsbetween the voltages applied, as described above.

Alternatively, a write “0” operation can be performed by putting thesilicon controlled rectifier device into the blocking mode. This can beperformed by applying the following bias: a positive voltage is appliedto BL terminal 74, a positive voltage is applied to WL terminal 70, anda positive voltage is applied to the substrate terminal 78, whileleaving SL terminal 72 and BW terminal 76 floating. Under theseconditions the voltage difference between anode and cathode, defined bythe voltages at substrate terminal 78 and BL terminal 74, will becometoo small to maintain the SCR device in conducting mode. As a result,the SCR device of cell 50 will be turned off. In one particularnon-limiting embodiment, a voltage of about +0.8 volts is applied toterminal 74, a voltage of about +0.5 volts is applied to terminal 70,and about +0.8 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

A holding or standby operation is implemented to enhance the dataretention characteristics of the memory cells 50. The holding operationcan be performed by applying the following bias: a substantially neutralvoltage is applied to BL terminal 74, a neutral or negative voltage isapplied to WL terminal 70, and a positive voltage is applied to thesubstrate terminal 78, while leaving SL terminal 72 and BW terminal 76floating. Under these conditions, if memory cell 50 is in memory/datastate “1” with positive voltage in floating body 24, the SCR device ofmemory cell 50 is turned on, thereby maintaining the state “1” data.Memory cells in state “0” will remain in blocking mode, since thevoltage in floating body 24 is not substantially positive and thereforefloating body 24 does not turn on the SCR device. Accordingly, currentdoes not flow through the SCR device and these cells maintain the state“0” data. In this way, an array of memory cells 50 can be refreshed byperiodically applying a positive voltage pulse through substrateterminal 78. Those memory cells 50 that are commonly connected tosubstrate terminal 78 and which have a positive voltage in body region24 will be refreshed with a “1” data state, while those memory cells 50that are commonly connected to the substrate terminal 78 and which donot have a positive voltage in body region 24 will remain in blockingmode, since their SCR device will not be turned on, and therefore memorystate “0” will be maintained in those cells. In this way, all memorycells 50 commonly connected to the substrate terminal will bemaintained/refreshed to accurately hold their data states. This processoccurs automatically, upon application of voltage to the substrateterminal 78, in a parallel, non-algorithmic, efficient process. In oneparticular non-limiting embodiment, a voltage of about 0.0 volts isapplied to terminal 74, a voltage of about −1.0 volts is applied toterminal 70, and about +0.8 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships therebetween.

When power down is detected, e.g., when a user turns off the power tocell 50, or the power is inadvertently interrupted, or for any otherreason, power is at least temporarily discontinued to cell 50, datastored in the floating body region 24 is transferred to the resistancechange memory 40. This operation is referred to as “shadowing” and isdescribed with reference to FIGS. 16A-16B.

To perform a shadowing process, a positive voltage is applied toterminal 72 and a substantially neutral voltage is applied to terminal74. A neutral voltage or slightly positive voltage is applied terminal70, a low positive voltage is applied to terminal 76, and asubstantially neutral voltage is applied to terminal 78. These voltagelevels can be driven by the appropriate circuitry controlling the memorycell array when the power shutdown is expected (such as during standbyoperation or when entering power savings mode) or from externalcapacitors in the event of abrupt and sudden power interruption.

When the floating body has a positive potential, the bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74 willbe turned on (FIG. 16A). The positive voltage applied to terminal 72 iscontrolled (e.g., varied to maintain a constant current) such that theelectrical current flowing through the resistance change memory 40 issufficient to change the state of the materials from a low resistivitystate to a high resistivity state. In the case of phase changematerials, this involves the change of the crystallinity of thechalcogenide materials from crystalline state to amorphous state, whilein metal oxide materials, this typically involves the annihilation ofconductive filaments. Accordingly, the non-volatile resistance changematerial will be in a high resistivity state when the volatile memory ofcell 50 is in state “1” (i.e. floating body 24 is positively charged).

When the floating body is neutral or negatively charged, the bipolartransistor formed by the SL terminal 72, floating body 24, and BLterminal 74 will be turned off (FIG. 16B). Therefore, when voltages areapplied as described above, no electrical current will flow through theresistance change memory 40 and it will retain its low resistivitystate. Accordingly, the non-volatile resistance change material will bein a low resistivity state when the volatile memory of cell 50 is instate “0” (i.e. floating body is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 72, a constant current of about 700 μA isapplied to terminal 74, about +1.0 volts is applied to terminal 70,about +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage and current levels mayvary, while maintaining the relative relationships between the chargesapplied, as described above. To change the non-volatile phase changememory from low resistivity state to high resistivity state, a currentlevel between 600 μA and 1 mA can be used. Lower current will be neededas the phase change material is scaled to smaller geometry. The currentlevels employed in metal oxide systems vary greatly depending on thematerials used, ranging from tens of microamperes to tens ofmilliamperes.

Note that this process occurs non-algorithmically, as the state of thefloating body 24 does not have to be read, interpreted, or otherwisemeasured to determine what state to write the non-volatile resistancechange memory 40 to. Rather, the shadowing process occurs automatically,driven by electrical potential differences. Accordingly, this process isorders of magnitude faster than one that requires algorithmicintervention.

When power is restored to cell 50, the state of the cell 50 as stored onthe non-volatile resistance change memory 40 is restored into floatingbody region 24. The restore operation (data restoration fromnon-volatile memory to volatile memory) is described with reference toFIGS. 17A-17B. In one embodiment, to perform the restore operation, anegative voltage is applied to terminal 70, a positive voltage isapplied to terminal 74, a negative voltage is applied to terminal 72, alow positive voltage is applied to terminal 76, and a substantiallyneutral voltage is applied to terminal 78.

This condition will result in result in band-to-band tunneling holeinjection into the floating body 24 (see FIG. 17A). However, if theresistance change memory is in low resistivity state, the negativevoltage applied to terminal 72 will evacuate holes in the floating body24 (see FIG. 17B) because the p-n junction formed by the floating body24 and the region 18 is forward-biased. Consequently, the volatilememory state of memory cell 50 will be restored to state “0” uponcompletion of the restore operation, restoring the state that the memorycell 50 held prior to the shadowing operation.

If the resistance change memory 40 is in high resistivity state, nocurrent flows through the resistance change memory 40, hence the holesaccumulated in the floating body 24 will not be evacuated (FIG. 17A). Asa result, the memory state “1” that the memory cell 50 held prior to theshadowing operation will be restored.

In one particular non-limiting example of this embodiment, about −1.0volts is applied to terminal 72, about +2.0 volts is applied to terminal74, about −1.2 volts is applied to terminal 70, about +0.6 volts isapplied to terminal 76, and a neutral voltage is applied to thesubstrate terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above.

Note that this process occurs non-algorithmically, as the state of thenon-volatile resistance change memory 40 does not have to be read,interpreted, or otherwise measured to determine what state to restorethe floating body 24 to. Rather, the restoration process occursautomatically, driven by resistivity state differences. Accordingly,this process is orders of magnitude faster than one that requiresalgorithmic intervention.

After restoring the memory cell(s) 50, the resistance change memory(ies)40 is/are reset to a predetermined state, e.g., a low resistivity stateas illustrated in FIG. 18, so that each resistance change memory 40 hasa known state prior to performing another shadowing operation.

To perform a reset operation according to the embodiment of FIG. 18, aneutral or slightly positive voltage is applied to terminal 70, asubstantially neutral voltage is applied to BL terminal 74, a positivevoltage is applied to SL terminal 72, a positive voltage is applied toterminal 76, and a neutral voltage is applied to substrate terminal 78.

When the floating body has a positive potential, the bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74 willbe turned on. The positive voltage applied to terminal 72 is controlled(e.g., varied to maintain a constant current) such that the electricalcurrent flowing through the resistance change memory 40 is sufficient tochange the resistivity of the resistance change materials from a highresistivity state to a low resistivity state. The voltage applied toterminal 72 initially has to exceed a threshold value (sometimesreferred to as ‘dynamic threshold voltage’) to ensure that allresistance change memory materials (including ones in high resistivitystate) are conducting. Accordingly, all the non-volatile resistancechange memory 40 will be in a low resistivity state upon completion ofthe reset operation.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, a constant current of about 400 μA isapplied to terminal 72, about +1.0 volts is applied to terminal 70, andabout +0.6 volts is applied to terminal 76. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above. The dynamic threshold voltageof a phase change non-volatile memory is typically greater than 1.0volts, upon which the high resistivity phase change materials willbecome conducting. The current level required to change phase changememory materials to low resistivity state typically range between 100 μAto 600 μA. For the case of metal oxide systems, the threshold voltageand the current level vary depending on the materials.

In another embodiment, the resistance change memory 40 is initialized tohave a high resistivity state. When power is applied to cell 50, cell 50operates like a capacitorless DRAM cell. In a capacitorless DRAM device,the memory information (i.e., data that is stored in memory) is storedas charge in the floating body of the transistor, i.e., in the body 24of cell 50. The presence of the electrical charge in the floating body24 modulates the threshold voltage of the cell 50, which determines thestate of the cell 50.

A read operation can be performed on memory cell 50 through thefollowing exemplary bias condition. A neutral voltage is applied to thesubstrate terminal 78, a neutral or positive voltage is applied to theBW terminal 76, a substantially neutral voltage is applied to SLterminal 72, a positive voltage is applied to BL terminal 74, and apositive voltage more positive than the voltage applied to BL terminal74 is applied to WL terminal 70. If cell 50 is in a state “1” havingholes in the body region 24, then a lower threshold voltage (gatevoltage where the transistor is turned on) is observed compared to thethreshold voltage observed when cell 50 is in a state “0” having noholes in body region 24. In one particular non-limiting embodiment,about 0.0 volts is applied to terminal 72, about +0.4 volts is appliedto terminal 74, about +1.2 volts is applied to terminal 70, about +0.6volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78. However, these voltage levels may vary, while maintainingthe relative relationships between the voltages applied, as describedabove.

Alternatively, a neutral voltage is applied to the substrate terminal78, a neutral or positive voltage is applied to the BW terminal 76, apositive voltage is applied to BL terminal 74, and SL terminal 72 isleft floating or grounded, and a neutral or positive voltage lesspositive than the positive voltage applied to BL terminal 74 is appliedto WL terminal 70. If cell 50 is in a state “1” having holes in the bodyregion 24, then the bipolar transistor formed by BL junction 16,floating body 24, and buried layer 22 is turned on. As a result, ahigher cell current is observed compared to when cell 50 is in a state“0” having no holes in body region 24. In one particular non-limitingembodiment, terminal 72 is left floating, about +3.0 volts is applied toterminal 74, about +0.5 volts is applied to terminal 70, about +0.6volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78. However, these voltage levels may vary while maintainingthe relative relationships between the voltages applied, as describedabove.

In another embodiment of the read operation that can be performed onmemory cell 50, a positive voltage is applied to the substrate terminal78, a neutral voltage is applied to BL terminal 74, SL terminal 72 isleft floating or grounded, a neutral or positive voltage is applied toWL terminal 70, while BW terminal 76 is left floating. If cell 50 is instate “1” with the body region 24 positively charged, the siliconcontrolled rectifier (SCR) device formed by the substrate 12, buriedwell 22, floating body 24, and the BL junction 74 will be turned on anda higher cell current is observed compared to when cell 50 is in a state“0” with the body region 24 in neutral state or negatively charged. Inone particular non-limiting embodiment, about +0.8 volts is applied toterminal 78, about +0.5 volts is applied to terminal 70, and about 0.0volts is applied to terminal 74, while terminals 72 and 76 are leftfloating. However, these voltage levels may vary while maintaining therelative relationships between the voltages applied, as described above.

The following conditions describe a write state “1” operation that canbe performed on memory cell 50, where the resistance change memory 40 isin a high resistivity state. To write state “1” using a band-to-bandtunneling mechanism, the following voltages are applied to theterminals: a positive voltage is applied to BL terminal 74, SL terminal72 is left floating or grounded, a negative voltage is applied to WLterminal 70, a neutral or positive voltage is applied to the BW terminal76, and a neutral voltage is applied to the substrate terminal 78. Underthese conditions, holes are injected from BL junction 16 into thefloating body region 24, leaving the body region 24 positively charged.In one particular non-limiting embodiment, about +2.0 volts is appliedto terminal 74, about −1.2 volts is applied to terminal 70, about +0.6volts is applied to terminal 76, about 0.0 volts is applied to terminal78, and terminal 72 is left floating. However, these voltage levels mayvary while maintaining the relative relationships between the voltagesapplied, as described above.

Alternatively, to write state “1” using an impact ionization mechanism,the following voltages are applied to the terminals: a positive voltageis applied to BL terminal 74, SL terminal 72 is left floating orgrounded, a positive voltage is applied to WL terminal 70, a neutral orpositive voltage is applied to BW terminal 76, and a substantiallyneutral voltage is applied to the substrate terminal 78. Under theseconditions, holes are injected from BL junction 16 into the floatingbody region 24, leaving the body region 24 positively charged. In oneparticular non-limiting embodiment, a potential of about +2.0 volts isapplied to terminal 74, a potential of about +0.5 volts is applied toterminal 70, a potential of about +0.6 volts is applied to terminal 76,and about 0.0 volts is applied to terminal 78, while terminal 72 is leftfloating. However, these voltage levels may vary while maintaining therelative relationships between the voltages applied, as described above.

Alternatively, the silicon controlled rectifier device can be operatedto put cell 50 into a state “1” by applying the following bias: asubstantially neutral voltage is applied to BL terminal 74, a positivevoltage is applied to WL terminal 70, and a positive voltage is appliedto the substrate terminal 78, while SL terminal 72 and BW terminal 76are left floating. The positive voltage applied to the WL terminal 70will increase the potential of the floating body 24 through capacitivecoupling and create a feedback process that turns the device on. In oneparticular non-limiting embodiment, a charge of about 0.0 volts isapplied to terminal 74, a charge of about +0.5 volts is applied toterminal 70, and about +3.0 volts is applied to terminal 78. However,these voltage levels may vary while maintaining the relativerelationships between the voltages applied, as described above.

A write “0” operation of the cell 50 is now described. To write “0” tocell 50, a negative bias is applied to BL terminal 74, SL terminal 72 isgrounded or left floating, a neutral or negative voltage is applied toWL terminal 70, a neutral or positive voltage is applied to BW terminal76, and a substantially neutral voltage is applied to substrate terminal78. Under these conditions, the p-n junction (junction between 24 and18) is forward-biased, evacuating any holes from the floating body 24.In one particular non-limiting embodiment, about −2.0 volts is appliedto terminal 74, about −1.2 volts is applied to terminal 70, about 0.0volts is applied to terminal 76, and about 0.0 volts is applied toterminal 78, while terminal 72 is grounded or left floating. However,these voltage levels may vary while maintaining the relativerelationships between the voltages applied, as described above.

In an alternate write “0” operation, a neutral voltage is applied to BLterminal 74, a positive voltage is applied to WL terminal 70, a neutralor positive voltage is applied to BW terminal 76, a substantiallyneutral voltage is applied to substrate terminal 78, while terminal 72is grounded or left floating. Under these conditions, holes from thefloating body 24 are evacuated. In one particular non-limitingembodiment, about +1.5 volts is applied to terminal 70, about 0.0 voltsis applied to terminal 74, about 0.0 volts is applied to terminal 76,about 0.0 volts is applied to terminal 78, while terminal 72 is groundedor left floating. However, these voltage levels may vary whilemaintaining the relative relationships between the voltages applied, asdescribed above.

Alternatively, a write “0” operation can be performed by putting thesilicon controlled rectifier device of cell 50 into the blocking mode.This can be performed by applying the following bias: a positive voltageis applied to BL terminal 74, a positive voltage is applied to WLterminal 70, and a positive voltage is applied to the substrate terminal78, while leaving SL terminal 72 and BW terminal 76 floating. In oneparticular non-limiting embodiment, a charge of about +0.8 volts isapplied to terminal 74, a charge of about +0.5 volts is applied toterminal 70, and about +0.8 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above.

A holding or standby operation is implemented to enhance the dataretention characteristics of the memory cells 50. The holding operationcan be performed by applying the following bias: a substantially neutralvoltage is applied to BL terminal 74, a neutral or negative voltage isapplied to WL terminal 70, and a positive voltage is applied to thesubstrate terminal 78, while leaving SL terminal 72 and BW terminal 76floating. Under these conditions, if memory cell 50 is in memory/datastate “1” with positive voltage in floating body 24, the SCR device ofmemory cell 50 is turned on, thereby maintaining the state “1” data.Memory cells in state “0” will remain in blocking mode, since thevoltage in floating body 24 is not substantially positive and thereforefloating body 24 does not turn on the SCR device. Accordingly, currentdoes not flow through the SCR device and these cells maintain the state“0” data. In this way, an array of memory cells 50 can be refreshed byperiodically applying a positive voltage pulse through substrateterminal 78. Those memory cells 50 that are commonly connected tosubstrate terminal 78 and which have a positive voltage in body region24 will be refreshed with a “1” data state, while those memory cells 50that are commonly connected to the substrate terminal 78 and which donot have a positive voltage in body region 24 will remain in blockingmode, since their SCR device will not be turned on, and therefore memorystate “0” will be maintained in those cells. In this way, all memorycells 50 commonly connected to the substrate terminal will bemaintained/refreshed to accurately hold their data states. This processoccurs automatically, upon application of voltage to the substrateterminal 78, in a parallel, non-algorithmic, efficient process. In oneparticular non-limiting embodiment, a voltage of about 0.0 volts isapplied to terminal 74, a voltage of about −1.0 volts is applied toterminal 70, and about +0.8 volts is applied to terminal 78. However,these voltage levels may vary, while maintaining the relativerelationships therebetween.

To perform a shadowing process on memory cell 50, a positive voltage isapplied to terminal 72 and a substantially neutral voltage is applied toterminal 74. A neutral voltage or positive voltage is applied terminal70 and a low positive voltage is applied to terminal 76, while thesubstrate terminal 78 is grounded.

When the floating body has a positive potential, the bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74and/or BW terminal 76 will be turned on. The positive voltage applied toterminal 72 is controlled (e.g., varied to maintain a constant current)such that the electrical current flowing through the resistance changememory 40 is sufficient to change the resistivity of the materials froma high resistivity state to a low resistivity state. The voltage appliedto terminal 72 initially has to exceed the dynamic threshold voltage(typically larger than 1.0 volts) to ensure that the resistance changememory 40 (even if it is in high resistivity state) will be conducting.Accordingly, the non-volatile resistance change material will be in alow resistivity state when the volatile memory of cell 50 is in state“1” (i.e. floating body 24 is positively charged).

When the floating body is neutral or negatively charged, the bipolartransistor formed by the SL terminal 72, floating body 24, and BLterminal 74 and/or BW terminal 76 will be turned off. Therefore, whenvoltages are applied as described above, no electrical current will flowthrough the resistance change memory 40 and it will retain its highresistivity state. Accordingly, the non-volatile resistance changematerial will be in a high resistivity state when the volatile memory ofcell 50 is in state “0” (i.e. floating body is neutral or negativelycharged).

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, a constant current of about 400 μA isapplied to terminal 72, about +1.0 volts is applied to terminal 70,about +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage and current levels mayvary, while maintaining the relative relationships between the chargesapplied, as described above. The current level required to change phasechange memory materials to low resistivity state typically range between100 μA to 600 μA, while that of metal oxide systems vary depending onthe materials. The current level is expected to decrease as theresistance change material is scaled to smaller geometry.

In another embodiment, the following bias can be applied: a neutralvoltage is applied to terminal 72, a neutral voltage or positive voltageis applied to terminal 70, a positive voltage is applied to terminal 78,while terminals 74 and 76 are left floating. When the floating body 24has a positive potential, the silicon controlled rectifier device formedby the SL 72 junction, floating body 24, buried layer 22, and substrate12 will be turned on. The positive voltage applied to terminal 78 iscontrolled (e.g., varied to maintain a constant current) such that theelectrical current flowing through the resistance change memory 40 issufficient to change the resistivity of the materials from a highresistivity state to a low resistivity state. For phase changematerials, the crystalline state changes from amorphous phase tocrystalline phase, while in metal oxide systems, this typically involvesthe formation of conductive filaments. Accordingly, the non-volatileresistance change material will be in a low resistivity state when thevolatile memory of cell 50 is in state “1” (i.e. floating body 24 ispositively charged).

When the floating body 24 is neutral or negatively charged, the siliconcontrolled rectifier device will be turned off. Therefore, no electricalcurrent flows through the resistance change memory 40 and it will retainits high resistivity state. Accordingly, the non-volatile resistancechange material will be in a high resistivity state when the volatilememory of cell 50 is in state “0” (i.e. floating body 24 is neutral ornegatively charged).

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 72, a constant current of about 400 μA isapplied to terminal 78, about +1.0 volts is applied to terminal 70,while terminals 74 and 76 are left floating. However, these voltagelevels may vary while maintaining the relative relationships between thevoltages applied, as described above. The current level required tochange phase change memory materials to low resistivity state typicallyrange between 100 μA to 600 μA and is expected to decrease as the phasechange memory is being scaled to smaller dimension. In metal oxidesystems, it varies depending on the materials used.

The restore operation (data restoration from non-volatile memory tovolatile memory) is now described. In one embodiment, to perform therestore operation, a negative voltage is applied to terminal 70, apositive voltage is applied to terminal 72, a neutral voltage is appliedto terminal 74, a neutral or low positive voltage is applied to terminal76, and a substantially neutral voltage is applied to terminal 78.

If the resistance change memory 40 is in low resistivity state, thiscondition will result in holes being injected into the floating body 24,generated through the band-to-band tunneling mechanism, therebyrestoring the state “1” that the memory cell 50 held prior to theshadowing operation. If the resistance change memory 40 is in highresistivity state, no holes will be generated; consequently, thevolatile memory state of memory cell 50 will be restored to state “0”.Upon completion of the restore operation, the volatile memory of cell 50is restored to the state that the volatile memory of memory cell 50 heldprior to the shadowing operation.

In one particular non-limiting example of this embodiment, about +2.0volts is applied to terminal 72, about +0.0 volts is applied to terminal74, about −1.2 volts is applied to terminal 70, about 0.0 volts isapplied to terminal 76, and about 0.0 volts is applied to terminal 78.However, these voltage levels may vary, while maintaining the relativerelationships between the charges applied, as described above.

In another embodiment of the restore operation, the following bias canbe applied: a neutral voltage is applied to terminal 72, a positivevoltage is applied to terminal 70, a positive voltage is applied toterminal 78, while terminals 74 and 76 are left floating. The positivevoltage applied to the WL terminal 70 will increase the potential of thefloating body 24 through capacitive coupling. If the resistance changememory 40 is in a low resistivity state, this will create a feedbackprocess that latches the device on and the volatile state of the memorycell 50 will be in state “1”. If the resistance change memory 40 is in ahigh resistivity state, the volatile state of the memory cell 50 willremain in state “0”. In one particular non-limiting embodiment, a chargeof about 0.0 volts is applied to terminal 72, a charge of about +0.5volts is applied to terminal 70, about +0.8 volts is applied to terminal78, while terminals 74 and 76 are left floating. However, these voltagelevels may vary while maintaining the relative relationships between thevoltages applied, as described above.

After restoring the memory cell(s) 50, the resistance change memory 40is/are reset to a high resistivity state, so that each resistance changememory 40 has a known state prior to performing another shadowingoperation.

To perform a reset operation according to one embodiment, a neutralvoltage or positive voltage is applied to terminal 70, a substantiallyneutral voltage is applied to BL terminal 74, a positive voltage isapplied to SL terminal 72, a neutral or positive voltage is applied toterminal 76, and a substantially neutral voltage is applied to terminal78.

When the floating body 24 has a positive potential, the bipolartransistor formed by the SL terminal 72, floating body 24, and BLterminal 74 and/or BW terminal 76 will be turned on. The positivevoltage applied to terminal 72 is controlled (e.g., varied to maintain aconstant current) such that the electrical current flowing through theresistance change memory 40 is sufficient to change the resistivity ofthe materials from a low resistivity state to a high resistivity state.Accordingly, all the non-volatile resistance change memory 40 will be ina high resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, a constant current of about 700 μA isapplied to terminal 72, about +1.0 volts is applied to terminal 70,about +0.6 volts is applied to terminal 76, and about 0.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. To change the non-volatile phase change memory from lowresistivity state to high resistivity state, a current level between 600μA and 1 mA can be used. Lower current will be needed as the phasechange material is scaled to smaller geometry.

In an alternative embodiment of the reset operation, the following biascan be applied: a neutral voltage is applied to terminal 72, a neutralvoltage or positive voltage is applied to terminal 70, a positivevoltage is applied to terminal 78, while terminals 74 and 76 are leftfloating.

When the floating body 24 has a positive potential, the siliconcontrolled rectifier device formed by the SL 72 junction, floating body24, buried layer 22, and substrate 12 will be turned on. The positivevoltage applied to terminal 78 is controlled (e.g., varied to maintain aconstant current) such that the electrical current flowing through theresistance change memory 40 is sufficient to change the resistivity ofthe materials from a low resistivity state to a high resistivity state.Accordingly, the non-volatile resistance change material will be in ahigh resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 72, a constant current of about 700 μA isapplied to terminal 78, about +1.0 volts is applied to terminal 70,while terminals 74 and 76 are left floating. However, these voltagelevels may vary while maintaining the relative relationships between thevoltages applied, as described above. To change the non-volatile phasechange memory from low resistivity state to high resistivity state, acurrent level between 600 μA and 1 mA can be used. Lower current will beneeded as the phase change material is scaled to smaller geometry.

In this embodiment of the memory cell operations, the volatile memoryoperations can be performed in the same manner regardless of the stateof the resistance change memory, i.e. there is no interference from thenon-volatile memory state to the volatile memory operations. Analternative embodiment of the memory cell operations is described inflowchart 200 in FIG. 24. At event 202, when power is applied to thememory device, the memory device can be operated without thenon-volatile memory of the device being set to a predetermined knownstate. The memory device may operate in the same manner as a volatilememory cell upon restore operation 208. As a result, the memory cell 50can operate into the volatile operation mode faster, without firstresetting the non-volatile memory state. The reset operation 204 can beperformed just prior to writing new data into the non-volatile memorycell during the shadowing operation 206. In an alternative embodiment,the volatile and non-volatile memory can be configured to storedifferent data, for example when the non-volatile memory is being usedto store “permanent data”, which does not change in value during routineuse. For example, this includes operating system image, applications,multimedia files, etc. The volatile memory can be used to store statevariable. In this embodiment, the reset operation 204 can be bypassed.

FIGS. 19A-19B show another embodiment (perspective, cross-sectional viewand top view, respectively) of the memory cell 50 described in thisinvention. In this embodiment, cell 50 has a fin structure 52 fabricatedon substrate 12, so as to extend from the surface of the substrate toform a three-dimensional structure, with fin 52 extending substantiallyperpendicularly to, and above the top surface of the substrate 12. Finstructure 52 is conductive and is built on buried well layer 22. Buriedwell layer 22 is also formed by an ion implantation process on thematerial of substrate 12. Buried well layer 22 insulates the floatingsubstrate region 24, which has a first conductivity type, from the bulksubstrate 12. Fin structure 52 includes first and second regions 16, 18having a second conductivity type. Thus, the floating body region 24 isbounded by the top surface of the fin 52, the first and second regions16, 18 the buried well layer 22, and insulating layers 26. Insulatinglayers 26 insulate cell 50 from neighboring cells 50 when multiple cells50 are joined to make a memory device. Fin 52 is typically made ofsilicon, but may comprise germanium, silicon germanium, galliumarsenide, carbon nanotubes, or other semiconductor materials known inthe art.

Device 50 further includes gates 60 on three sides of the floatingsubstrate region 24 as shown in FIG. 19A. Alternatively, gates 60 canenclose two opposite sides of the floating substrate region 24. Gates 60are insulated from floating body 24 by insulating layers 62. Gates 60are positioned between the first and second regions 16, 18, adjacent tothe floating body 24.

A resistance change memory element 40 is positioned above the regionhaving second conductivity type. The resistance change memory element 40is shown as a variable resistor, and may be formed from resistancechange memory element known in the art. In one embodiment, thenon-volatile memory is initialized to have a low resistance state. Inanother alternate embodiment, the non-volatile memory is initialized tohave a high resistance state.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, bit line (BL) terminal 74, buried well (BW)terminal 76 and substrate terminal 78. Terminal 70 is connected to thegate 60. Terminal 74 is connected to first region 16 and terminal 72 isconnected to resistance change memory element 40, which is, in turn,connected to second region 18. Alternatively, terminal 74 can beconnected to resistance change memory element 40 and terminal 72 can beconnected to first region 16. Terminal 76 is connected to buried layer22 and terminal 78 is connected to substrate 12.

The operations of the embodiment of memory cell 50 shown in FIGS.19A-19B are the same as those described above with regard to theembodiment of memory cell 50 of FIG. 12. Equivalent terminals have beenassigned with the same numbering labels in both figures.

FIG. 20 illustrates another embodiment of the memory cell 50 fabricatedon a silicon-on-insulator (SOI) substrate. The cell 50 includes asubstrate 12 of a first conductivity type, such as a p-type conductivitytype, for example. Substrate 12 is typically made of silicon, but maycomprise germanium, silicon germanium, gallium arsenide, carbonnanotubes, or other semiconductor materials known in the art. Thesubstrate 12 has a surface 14. A first region 16 having a secondconductivity type, such as n-type, for example, is provided in substrate12 and which is exposed at surface 14. A second region 18 having thesecond conductivity type is also provided in substrate 12, which isexposed at surface 14 and which is spaced apart from the first region16. First and second regions 16 and 18 are formed by an implantationprocess formed on the material making up substrate 12, according to anyof implantation processes known and typically used in the art. A buriedinsulator layer 22 insulates the body region 24 from the substrate 12.The body region 24 is bounded by surface 14, first and second regions 16and 18, and the buried insulator layer 22. The buried insulator layer 22may be buried oxide (BOX).

A gate 60 is positioned in between the regions 16 and 18, and above thesurface 14. The gate 60 is insulated from surface 14 by an insulatinglayer 62. Insulating layer 62 may be made of silicon oxide and/or otherdielectric materials, including high-K dielectric materials, such as,but not limited to, tantalum peroxide, titanium oxide, zirconium oxide,hafnium oxide, and/or aluminum oxide. The gate 60 may be made ofpolysilicon material or metal gate electrode, such as tungsten,tantalum, titanium and their nitrides.

A resistance change memory element 40 is positioned above the regionhaving second conductivity type 16. The resistance change memory element40 is shown as a variable resistor, and may be formed from phase changematerial or metal-insulator-metal systems as described in previousembodiments above.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, bit line (BL) terminal 74, and substrate terminal78. Terminal 70 is connected to the gate 60. Terminal 74 is connected tofirst region 16 and terminal 72 is connected to resistance change memoryelement 40 which is connected to second region 18. Alternatively,terminal 74 can be connected to resistance change memory element 40 andterminal 72 can be connected to first region 16. Terminal 78 isconnected to substrate 12.

When power is applied to cell 50, cell 50 operates like a capacitorlessDRAM cell. In a capacitorless DRAM device, the memory information (i.e.,data that is stored in memory of the cells) is stored as charge in thefloating bodies 24 of the transistors, i.e., in the bodies 24 of cells50. The presence of the electrical charge in the floating body 24modulates the threshold voltage of the cell 50, which determines thestate of the cell 50. In one embodiment, the non-volatile memory isinitialized to have a low resistance state.

To perform a read operation on memory cell 50 according to oneembodiment of the present invention, a neutral or negative voltage isapplied to the substrate terminal 78, a substantially neutral voltage isapplied to SL terminal 72, a positive voltage is applied to BL terminal74, and a positive voltage more positive than the positive voltageapplied to BL terminal 74 is applied to WL terminal 70. If cell 50 is ina state “1” having holes in the body region 24, then a lower thresholdvoltage (gate voltage where the transistor is turned on) is observedcompared to the threshold voltage observed when cell 50 is in a state“0” having substantially no holes in body region 24. In one particularnon-limiting embodiment, about 0.0 volts is applied to terminal 72,about +0.4 volts is applied to terminal 74, about +1.2 volts is appliedto terminal 70, and about −2.0 volts is applied to terminal 78. However,these voltage levels may vary while maintaining the relativerelationships between the voltages applied, as described above.

Alternatively, a neutral or negative voltage is applied to the substrateterminal 78, a substantially neutral voltage is applied to SL terminal72, a positive voltage is applied to BL terminal 74, and a positivevoltage less positive than the positive voltage applied to BL terminal74 is applied to WL terminal 70. If cell 50 is in a state “1” havingholes in the body region 24, then the parasitic bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74 willbe turned on and a higher cell current is observed compared to when cell50 is in a state “0” having no holes in body region 24. In oneparticular non-limiting embodiment, about 0.0 volts is applied toterminal 72, about +3.0 volts is applied to terminal 74, about +0.5volts is applied to terminal 70, and about −2.0 volts is applied toterminal 78. However, these voltage levels may vary while maintainingthe relative relationships between the voltages applied, as describedabove.

A write state “1” operation can be carried out on cell 50 by performingband-to-band tunneling hot hole injection or impact ionization hot holeinjection. To write state “1” using band-to-band tunneling mechanism,the following voltages are applied to the terminals: a positive voltageis applied to BL terminal 74, a substantially neutral voltage is appliedto SL terminal 72, a negative voltage is applied to WL terminal 70, aneutral or negative voltage is applied to the substrate terminal 78.Under these conditions, holes are injected from BL terminal 74 into thefloating body region 24, leaving the body region 24 positively charged.In one particular non-limiting embodiment, a charge of about 0.0 voltsis applied to terminal 72, a potential of about +2.0 volts is applied toterminal 74, a potential of about −1.2 volts is applied to terminal 70,and about −2.0 volts is applied to terminal 78. However, these voltagelevels may vary while maintaining the relative relationships between thevoltages applied, as described above.

Alternatively, to write state “1” using an impact ionization mechanism,the following voltages are applied to the terminals: a positive voltageis applied to BL terminal 74, a substantially neutral voltage is appliedto SL terminal 72, a positive voltage is applied to WL terminal 70, anda neutral or negative voltage is applied to the substrate terminal 78.Under these conditions, holes are injected from the region 16 into thefloating body region 24, leaving the body region 24 positively charged.In one particular non-limiting embodiment, +0.0 volts is applied toterminal 72, a potential of about +2.0 volts is applied to terminal 74,a potential of about +0.5 volts is applied to terminal 70, and about−2.0 volts is applied to terminal 78. However, these voltage levels mayvary while maintaining the relative relationships between the voltagesapplied, as described above.

A write “0” operation of the cell 50 is now described. To write “0” tocell 50, a negative bias is applied to SL terminal 72 and/or BL terminal74, a neutral or negative voltage is applied to WL terminal 70, and aneutral or negative voltage is applied to substrate terminal 78. Underthese conditions, the p-n junction (junction between 24 and 16 andbetween 24 and 18) is forward-biased, evacuating any holes from thefloating body 24. In one particular non-limiting embodiment, about −1.0volts is applied to terminal 72, about −1.0 volts is applied to terminal70, and about 0.0 volts is applied to terminal 78. However, thesevoltage levels may vary, while maintaining the relative relationshipsbetween the voltages applied, as described above.

Alternatively, a write “0” operation can be performed to cell 50 byapplying a positive bias to WL terminal 70, and substantially neutralvoltages to SL terminal 72 and BL terminal 74, and a neutral or negativevoltage to substrate terminal 78. Under these conditions, the holes willbe removed from the floating body 24 through charge recombination. Inone particular non-limiting embodiment, about 1.0 volts is applied toterminal 70, about 0.0 volts are applied to terminals 72 and 74, andabout −2.0 volts is applied to terminal 78. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

To perform a shadowing process, a positive voltage is applied toterminal 72 and a substantially neutral voltage is applied to terminal74. A neutral voltage or positive voltage is applied terminal 70 and aneutral or negative voltage is applied to terminal 78.

When the floating body has a positive potential, the bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74 willbe turned on. The positive voltage applied to terminal 72 is controlled(e.g., varied to maintain a constant current) such that the electricalcurrent flowing through the resistance change memory 40 is sufficient tochange the resistivity of the materials from a low resistivity state toa high resistivity state. Accordingly, the non-volatile resistancechange material will be in a high resistivity state when the volatilememory of cell 50 is in state “1” (i.e. floating body 24 is positivelycharged).

When the floating body is neutral or negatively charged, the bipolartransistor formed by the SL terminal 72, floating body 24, and BLterminal 74 will be turned off. Therefore, when voltages are applied asdescribed above, no electrical current will flow through the resistancechange memory 40 and it will retain its low resistivity state.Accordingly, the non-volatile resistance change material will be in alow resistivity state when the volatile memory of cell 50 is in state“0” (i.e. floating body is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, about 700 μA is applied to terminal 72,about +1.0 volts is applied to terminal 70, and about −2.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. To change the non-volatile phase change memory from lowresistivity state to high resistivity state, a current level between 600μA and 1 mA can be used. The current level is expected to decrease asthe phase change material is scaled to smaller geometry.

Note that this process occurs non-algorithmically, as the state of thefloating body 24 does not have to be read, interpreted, or otherwisemeasured to determine what state to write the non-volatile resistancechange memory 40 to. Rather, the shadowing process occurs automatically,driven by electrical potential differences. Accordingly, this process isorders of magnitude faster than one that requires algorithmicintervention.

When power is restored to cell 50, the state of the cell 50 as stored onthe non-volatile resistance change memory 40 is restored into floatingbody region 24. In one embodiment, to perform the restore operation, anegative voltage is applied to terminal 70, a positive voltage isapplied to terminal 74, a negative voltage is applied to terminal 72,and a neutral or negative voltage is applied to terminal 78.

If the resistance change memory 40 is in high resistivity state, thiscondition will result in holes injection into the floating body 24,generated through the band-to-band tunneling mechanism, therebyrestoring the state “1” that the memory cell 50 held prior to theshadowing operation.

If the resistance change memory 40 is in low resistivity state, thenegative voltage applied to terminal 72 will evacuate holes injectedinto the floating body 24 because the p-n junction formed by thefloating body 24 and the region 16 is forward-biased. Consequently, thevolatile memory state of memory cell 50 will be restored to state “0”upon completion of the restore operation, restoring the state that thememory cell 50 held prior to the shadowing operation.

In one particular non-limiting example of this embodiment, about −1.0volts is applied to terminal 72, about +2.0 volts is applied to terminal74, about −1.2 volts is applied to terminal 70, and about −2.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above.

Note that this process occurs non-algorithmically, as the state of thenon-volatile resistance change memory 40 does not have to be read,interpreted, or otherwise measured to determine what state to restorethe floating body 24 to. Rather, the restoration process occursautomatically, driven by resistivity state differences. Accordingly,this process is orders of magnitude faster than one that requiresalgorithmic intervention.

After restoring the memory cell(s) 50, the resistance change memory 40is/are reset to a predetermined state, e.g., a low resistivity state, sothat each resistance change memory 40 has a known state prior toperforming another shadowing operation.

To perform a reset operation according to the present embodiment, aneutral voltage or positive voltage is applied to terminal 70, asubstantially neutral voltage is applied to BL terminal 74, a positivevoltage is applied to SL terminal 72, and a neutral or negative voltageis applied to terminal 78.

When the floating body has a positive potential, the bipolar transistorformed by the SL terminal 72, floating body 24, and BL terminal 74 willbe turned on. The positive voltage applied to terminal 72 is optimizedsuch that the electrical current flowing through the resistance changememory 40 is sufficient to change the resistivity of the materials froma high resistivity state to a low resistivity state. Accordingly, allthe non-volatile resistance change memory 40 will be in a lowresistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, about 400 μA is applied to terminal 72,about −1.0 volts is applied to terminal 70, and about −2.0 volts isapplied to terminal 78. However, these voltage levels may vary, whilemaintaining the relative relationships between the charges applied, asdescribed above. The current level required to change phase changememory materials to low resistivity state typically range between 100 μAto 600 μA. The current level requirement is expected to decrease as thephase change memory dimension is reduced.

FIG. 21 illustrates an alternative embodiment of a memory cell 50according to the present invention. In this embodiment, cell 50 has afin structure 52 fabricated on a silicon-on-insulator (SOI) substrate12, so as to extend from the surface of the substrate to form athree-dimensional structure, with fin 52 extending substantiallyperpendicularly to, and above the top surface of the substrate 12. Finstructure 52 is conductive and is built on buried insulator layer 22,which may be buried oxide (BOX). Insulator layer 22 insulates thefloating substrate region 24, which has a first conductivity type, fromthe bulk substrate 12. Fin structure 52 includes first and secondregions 16, 18 having a second conductivity type. Thus, the floatingbody region 24 is bounded by the top surface of the fin 52, the firstand second regions 16, 18 and the buried insulator layer 22. Fin 52 istypically made of silicon, but may comprise germanium, silicongermanium, gallium arsenide, carbon nanotubes, or other semiconductormaterials known in the art.

Device 50 further includes gates 60 on three sides of the floatingsubstrate region 24, as shown in FIG. 21. Alternatively, gates 60 canenclose two opposite sides of the floating substrate region 24. Gates 60are insulated from floating body 24 by insulating layers 62. Gates 60are positioned between the first and second regions 16, 18, adjacent tothe floating body 24.

A resistance change memory element 40 is positioned above the regionhaving second conductivity type. The resistance change memory element 40is shown as a variable resistor, and may be formed from phase changematerial or metal-insulator-metal systems, for example. In oneembodiment, the non-volatile memory is initialized to have a lowresistance state. In another alternate embodiment, the non-volatilememory is initialized to have a high resistance state.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, bit line (BL) terminal 74, and substrate terminal78. Terminal 70 is connected to the gate 60. Terminal 74 is connected tofirst region 16 and terminal 72 is connected to resistance change memoryelement 40 which is connected to second region 18. Alternatively,terminal 74 can be connected to resistance change memory element 40 andterminal 72 can be connected to first region 16. The bulk substrate 12is connected to terminal 78.

Cell 50 includes four terminals: word line (WL) terminal 70, source line(SL) terminal 72, bit line (BL) terminal 74 and substrate terminal 78.Gate 60 is connected to terminal 70, first and second regions 16, 18 areconnected to terminals 74 and 72, respectively, or vice versa, and thebulk substrate 12 is connected to terminal 78.

The operations of the embodiment of memory cell 50 shown in FIG. 21 arethe same as for memory cell 50 described in FIG. 20. Equivalentterminals have been assigned with the same numbering labels in bothfigures.

Up until this point, the description of cells 50 have been in regard tobinary cells, in which the data memories, both volatile andnon-volatile, are binary, meaning that they either store state “1” orstate “0”. However, in an alternative embodiment, any of the memory cellembodiments described herein can be configured to function asmulti-level cells, so that more than one bit of data can be stored ineach cell 50. FIG. 22 illustrates an example of voltage states of amulti-level cell wherein two bits of data can be stored in each cell 50.In this case, a voltage less than or equal to a first predeterminedvoltage and greater than a second predetermined voltage that is lessthan the first predetermined voltage in floating body or base region 24volts is interpreted as state “01”, a voltage less than or equal to thesecond predetermined voltage is interpreted as state “00”, a voltagegreater than the first predetermined voltage and less than or equal to athird predetermined voltage that is greater than the first predeterminedvoltage is interpreted to be state “10” and a voltage greater than thethird predetermined voltage is interpreted as state “11”.

During the shadowing operation, the potential of the floating body orbase region 24 in turn determines the amount of current flowing throughthe resistance change memory 40 or the floating gate 60, which will inturn determine the state of the non-volatile memory. The resistivitystate of the resistance change memory 40 or the charge stored on thefloating gate 60 can then be configured to store multi-level bits.

During restore operation, the resistivity state of the resistance changememory 40 or the charge of the floating gate 60 will subsequentlydetermine the voltage state of the floating body or base region 24.

FIG. 23A shows an example of array architecture 80 of a plurality ofmemory cells 50 arranged in a plurality of rows and columns according toan embodiment of the present invention. The memory cells 50 areconnected such that within each row, all of the gates 60 are connectedby a common word line terminal 70. The first regions 18 are connected toresistance change materials 40. Within the same row, they are thenconnected by a common source line 72. Within each column, the secondregions 16 are connected to a common bit line terminal 74. Within eachrow, all of the buried layers 22 are connected by a common buried wellterminal 76. Likewise, within each row, all of the substrates 12 areconnected by a common substrate terminal 78.

FIG. 23B shows an example of array architecture 80 of a plurality ofmemory cells 50 fabricated on a silicon-on-insulator (SOI) substrate,arranged in a plurality of rows and columns according to an embodimentof the present invention. The memory cells 50 are connected such thatwithin each row, all of the gates 60 are connected by a common word lineterminal 70. The first regions 18 are connected to resistance changematerials 40. Within the same row, they are then connected by a commonsource line 72. Within each column, the second regions 16 are connectedto a common bit line terminal 74. Likewise, within each row, all of thesubstrates 12 are connected by a common substrate terminal 78.

FIG. 25 is a schematic of an equivalent circuit model of a memory cell50 using a resistance change element 40 with a thin capacitively coupledthyristor (TCCT) access device 130 according to an embodiment of thepresent invention. TCCT device 130 includes four regions withalternating n-type and p-type conductivity, along with a gatecapacitively coupled to the p-region near the cathode terminal. In FIG.25, the TCCT device 130 is shown as a back-to-back diode 134 with a gateterminal 132. A resistive change memory 40 is used to store non-volatiledata, as it is able to retain its state in the absence of power.Examples of resistive change memory include phase change memory,conductive bridging memory, and metal oxide memory.

A plurality of memory cells 50 according to a non-limiting embodiment ofthe present invention is shown in FIG. 26, where a phase change elementis used to illustrate the resistive change memory. Memory cells 50 areformed vertically and are insulated from one another by insulator layers172. The vertical arrangement results in a compact cell size. Thep-n-p-n regions 168, 166, 164, and 162 forming the thyristor device 130are formed using semiconductor materials, such as silicon orpolysilicon. A gate 170 is capacitively coupled to the p-region 164. TheTCCT device 130 is formed on top of a conductor layer 160. The conductorlayer 160 can be made of semiconductor materials such as silicon,germanium, silicon germanium, gallium arsenide, carbon nanotubes, orother semiconductor materials, or conductor materials such as tungsten(W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formedby a bottom electrode 180, a chalcogenide material 182, and a topelectrode 184. The bottom electrode 180 can be made from titaniumnitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titaniumaluminum nitride (TiAlN) layer, or other electrode layer. Phase changematerial 182 is a material having properties, such as electricalresistance, that depend on the crystalline phase of the material.Crystalline phase will exhibit a low resistivity state and amorphousphase will exhibit a high resistivity state. Examples of phase changematerial include alloys containing elements from Column VI of theperiodic table, such as GeSbTe alloys. The top electrode layer 184 canbe formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 isconnected to the gate 170. Terminal 72 is connected to the phase changememory top electrode 184 and terminal 74 is connected to the conductorlayer 160.

The TCCT device 130 can operate in two modes: a low impedance conductingmode and a high impedance blocking mode. Gate 170 is used to assist theswitching between the two states by modifying the potential of the baseregion 164 through capacitive coupling. To select a resistive changememory element 40, the TCCT device 130 operates in a conducting mode.

The read operation of the memory cell 50 can be performed as follows. Apositive voltage is applied to the SL terminal 72, a substantiallyneutral voltage is applied to the BL terminal 74, and a positive voltageis applied to WL terminal 70. The positive voltage applied to the SLterminal 72 needs to be lower than the switching voltage of theresistive change element 40 to avoid unintentional writing of theresistive change element 40. If the resistive change element 40 is inhigh resistance state, no current will flow through the memory cell 50.If the resistive change element 40 is in low resistance state, a highercurrent will be observed flowing through the memory cell 50. In oneparticular non-limiting embodiment, about +0.5 volts is applied toterminal 72, about 0.0 volts is applied to terminal 74, and about +0.5volts is applied to terminal 70. However, these voltage levels may varywhile maintaining the relative relationships between the chargesapplied, as described above.

To write the phase change memory element 40 into a low resistance state,which is often referred to as “SET” state, the following bias isapplied. A positive voltage is applied to SL terminal 72, asubstantially neutral voltage is applied to the BL terminal 74, and apositive voltage is applied to WL terminal 70. The positive voltageapplied to terminal 72 is controlled so that the electrical currentflowing through the phase change memory 40 is substantially constant andis sufficient to change the phase of the materials to a low resistivitystate.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, about 400 μA is applied to terminal 72,and about +0.5 volts is applied to terminal 70. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

To write the phase change memory element 40 into a high resistancestate, which is often referred to as “RESET” state, the following biasis applied. A positive voltage is applied to SL terminal 72, asubstantially neutral voltage is applied to the BL terminal 74, and apositive voltage is applied to WL terminal 70. The positive voltageapplied to terminal 72 is controlled so that the electrical currentflowing through the phase change memory 40 is substantially constant andis sufficient to change the phase of the material to a low resistivitystate.

In one particular non-limiting example of this embodiment, about 0.0volts is applied to terminal 74, about 700 μA is applied to terminal 72,and about +0.5 volts is applied to terminal 70. However, these voltagelevels may vary, while maintaining the relative relationships betweenthe charges applied, as described above.

To increase the memory density, the memory cell 50 can be stacked in thevertical direction to form a three-dimensional memory array. FIG. 27shows an example of a three-dimensional memory array 150 according to anembodiment of the present invention, in which memory array 80,comprising a two-dimensional array of memory cells 50 (i.e., rows andcolumns of interconnected memory cells 50 (although only one planecorresponding to one row or one column is shown in FIG. 26, and only oneplane is likewise shown in FIG. 27) is stacked in the verticaldirection, insulated by an insulator layer 190. The insulation layer 190is typically made of silicon oxide, although other insulating materialscan be used.

FIG. 28 illustrates an example of memory array architecture of thememory array 150, where two vertical stacks of memory array 80 areshown. At each stack, the memory cells 50 are connected such that withineach row, all of the gates 170 are connected in common word lineterminals 70 and the conductor layer 160 is connected to the common bitline terminals 74. Within each column, the top electrodes 184 areconnected to common source line terminals 72. In another embodiment ofthe memory array architecture, the source line terminals 72 can beshared between the memory cells 50 in the first and second level of thestacks. In another embodiment, the gates 170 and WL terminals 70 cancontrol regions 164 of two adjacent vertical stacks in two adjacentcolumns. This will further reduce the size of memory array 150.

FIGS. 29-35 illustrate an embodiment of a sequence of fabrication stepsof the memory array 150. As shown in FIG. 29, a conductor layer 160 isdeposited on an insulator layer 190, followed by a polysilicon layer162. The polysilicon is doped to form n-type region, either through ionimplantation process or through in-situ deposition process. Theconductor layer 160 and the polysilicon layer 162 are then patterned andetched to form column lines of the memory array.

Subsequently, insulator layer 172 is deposited on the polysilicon layer162. Holes are then patterned and etched through the insulator layer172. Polysilicon films are then deposited to fill the holes, followed bya planarization step. An ion implantation process can then be performedto form the p-n-p regions 168, 166, and 164 shown in FIG. 30.

Following the formation of the p-n-p regions 168, 166 an 164, theinsulator layer 172 is patterned to form the row lines of the memoryarray and etched as shown in FIG. 31. A thin layer of insulating layer174 is then deposited as shown in FIG. 32. The insulator layer 174 istypically silicon oxide, but other insulating materials particularlywith high dielectric constants may be used. As shown in FIG. 33, this isthen followed by a polysilicon deposition step to form the gates 170. Aninsulating layer 176 is subsequently deposited following the polysilicon170 deposition. A chemical mechanical polish (CMP) or a dry etch processcan then be performed to planarize the resulting films.

As shown in FIG. 34, a bottom electrode 180, a phase change material182, and a top electrode 184 are subsequently deposited. These films arethen patterned and etched to form the row lines of the memory array. Aninsulating layer 290 is then deposited to cap the resulting layers, asdepicted in FIG. 35

Another embodiment of an array 80 of memory cells 50 is shown in FIG.36. Memory cells 50 are formed vertically and are insulated from oneanother by an insulator layer 172. The vertical arrangement results in acompact cell size. The p-n-p-n regions 168, 166, 164, and 162 formingthe thyristor device is formed using semiconductor materials, such assilicon or polysilicon. A gate 170 is capacitively coupled to andencloses the p-region 64. The TCCT device 130 is formed on top of aconductor layer 160. The conductor layer 160 can be made ofsemiconductor materials such as silicon, germanium, silicon germanium,gallium arsenide, carbon nanotubes, or other semiconductor materials, orconductor materials such as tungsten (W), aluminum (Al), titanium (Ti),or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formedby a bottom electrode 180, a chalcogenide material 182, and a topelectrode 184. The bottom electrode 180 can be made from titaniumnitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titaniumaluminum nitride (TiAlN) layer, or other electrode layer. Phase changematerial 182 is a material having properties, such as electricalresistance, that depend on the crystalline phase of the material.Crystalline phase will exhibit a low resistivity state and amorphousphase will exhibit a high resistivity state. Examples of phase changematerial include alloys containing elements from Column VI of theperiodic table, such as GeSbTe alloys. The top electrode layer 84 can beformed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 isconnected to the gate 170. Terminal 72 is connected to the phase changememory top electrode 184 and terminal 74 is connected to the conductorlayer 160.

To increase the memory density, the arrays 80 of memory cells 50 can bestacked in the vertical direction to form a three-dimensional memoryarray 150. In another embodiment, the gates 170 and WL terminals 70 cancontrol regions 164 of two adjacent vertical stacks in two adjacentcolumns. This will further reduce the memory array size.

Another embodiment of an array 80 of memory cells 50 is shown in FIG.37. Memory cells 50 are formed vertically and are insulated from oneanother by an insulator layer 172. The vertical arrangement results in acompact cell size. The p-n-p-n regions 168, 166, 164, and 162 formingthe thyristor device 130 is formed using semiconductor materials, suchas silicon or polysilicon. A gate 170 is capacitively coupled to thep-region 164. The TCCT device 130 is formed on top of a conductor layer160. The conductor layer 160 can be made of semiconductor materials suchas silicon, germanium, silicon germanium, gallium arsenide, carbonnanotubes, or other semiconductor materials, or conductor materials suchas tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formedby a bottom electrode 180, a chalcogenide material 182, and a topelectrode 184. The bottom electrode 180 can be made from titaniumnitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titaniumaluminum nitride (TiAlN) layer, or other electrode layer. Phase changematerial 182 is a material having properties, such as electricalresistance, that depend on the crystalline phase of the material.Crystalline phase will exhibit a low resistivity state and amorphousphase will exhibit a high resistivity state. Examples of phase changematerial include alloys containing elements from Column VI of theperiodic table, such as GeSbTe alloys. The top electrode layer 184 canbe formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 isconnected to the gate 170. Terminal 72 is connected to the phase changememory top electrode 184 and terminal 74 is connected to the conductorlayer 160.

To increase the memory density, the arrays 80 of memory cells 50 can bestacked in the vertical direction to form a three-dimensional memoryarray 150. In another embodiment, the gates 170 and WL terminals 70 cancontrol regions 164 of two adjacent vertical stacks in two adjacentcolumns. This will further reduce the memory array size.

Another embodiment of memory cells 50 is shown in FIG. 38. Memory cell50 is formed vertically and is insulated from one another by aninsulator layer 172. The vertical arrangement results in a compact cellsize. The p-n-p-n regions 168, 166, 164, and 162 forming the thyristordevice 130 is formed using semiconductor materials, such as silicon orpolysilicon. A gate 170 is capacitively coupled to and encloses thep-region 164. The TCCT device is formed on top of a conductor layer 160.The conductor layer 160 can be made of semiconductor materials such assilicon, germanium, silicon germanium, gallium arsenide, carbonnanotubes, or other semiconductor materials, or conductor materials suchas tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory on top of the thyristor device is formed by abottom electrode 180, a chalcogenide material 182, and a top electrode184. The bottom electrode 180 can be made from titanium nitride (TiN)layer, titanium silicon nitride (TiSiN) layer, titanium aluminum nitride(TiAlN) layer, or other electrode layer. Phase change material 182 is amaterial having properties, such as electrical resistance, that dependon the crystalline phase of the material. Crystalline phase will exhibita low resistivity state and amorphous phase will exhibit a highresistivity state. Examples of phase change materials that can be usedinclude alloys containing elements from Column VI of the periodic table,such as GeSbTe alloys. The top electrode layer 184 can be formed fromaluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, sourceline (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 isconnected to the gate 170. Terminal 72 is connected to the phase changememory top electrode 184 and terminal 74 is connected to the conductorlayer 160.

To increase the memory density, the arrays 80 of memory cells 50 can bestacked in the vertical direction to form a three-dimensional memoryarray 150. In another embodiment, the gates 170 and WL terminals 70 cancontrol regions 14 of two adjacent vertical stacks in two adjacentcolumns. This will further reduce the memory array size.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, material, composition of matter, process, processstep or steps, to the objective, spirit and scope of the presentinvention. All such modifications are intended to be within the scope ofthe claims appended hereto.

That which is claimed is:
 1. A semiconductor memory cell comprising: acapacitorless transistor having a floating body configured to store dataas charge therein when power is applied to said cell; and a nonvolatilememory comprising a resistance change element configured to store saiddata stored in said floating body upon transfer thereto.
 2. Thesemiconductor memory cell of claim 1, wherein said resistance changeelement comprises a phase change material.
 3. The semiconductor memorycell of claim 1, wherein said resistance change element comprises ametal-oxide-metal system.
 4. The semiconductor memory cell of claim 1,wherein said nonvolatile memory stores said data stored in said floatingbody upon receiving an instruction to back up said data stored in saidfloating body.
 5. The semiconductor memory cell of claim 1, wherein saidnonvolatile memory stores said data stored in said floating body upon aloss of power to said cell, wherein said cell is configured to perform ashadowing process whereby said data in said floating body is loaded intoand stored in said nonvolatile memory.
 6. The semiconductor memory cellof claim 5, wherein said loss of power to said cell is one ofunintentional power loss or intentional power loss, wherein saidintentional power loss is predetermined to conserve power.
 7. Thesemiconductor memory cell of claim 5, wherein, upon restoration of powerto said cell, said data in said nonvolatile memory is loaded into saidfloating body and stored therein.
 8. The semiconductor memory cell ofclaim 7, wherein said cell is configured to reset said nonvolatilememory to an initial state after loading said data into said floatingbody upon said restoration of power.
 9. A semiconductor memory cellcomprising: a capacitorless transistor having a floating body configuredto store data as charge therein when power is applied to said cell; anda nonvolatile memory comprising a resistance change element; whereincurrent flowing to said resistance change element flows through saidfloating body.
 10. The semiconductor memory cell of claim 9, whereinsaid resistance change element comprises a phase change material. 11.The semiconductor memory cell of claim 9, wherein said resistance changeelement comprises a metal-oxide-metal system.
 12. The semiconductormemory cell of claim 9, wherein said nonvolatile memory stores said datastored in said floating body upon receiving an instruction to back upsaid data stored in said floating body.
 13. The semiconductor memorycell of claim 9, wherein said nonvolatile memory stores said data storedin said floating body upon a loss of power to said cell, wherein saidcell is configured to perform a shadowing process whereby said data insaid floating body is loaded into and stored in said nonvolatile memory.14. The semiconductor memory cell of claim 13, wherein said loss ofpower to said cell is one of unintentional power loss or intentionalpower loss, wherein said intentional power loss is predetermined toconserve power.
 15. The semiconductor memory cell of claim 13, wherein,upon restoration of power to said cell, said data in said nonvolatilememory is loaded into said floating body and stored therein.
 16. Thesemiconductor memory cell of claim 15, wherein said cell is configuredto reset said nonvolatile memory to an initial state after loading saiddata into said floating body upon said restoration of power.
 17. Asemiconductor memory cell comprising: a capacitorless transistor havinga floating body configured to store data as charge therein when power isapplied to said cell; and a nonvolatile memory comprising a resistancechange element, wherein an amount of current flowing to said resistancechange element is determined by said charge stored in said floatingbody.
 18. The semiconductor memory cell of claim 17, wherein saidresistance change element comprises a phase change material.
 19. Thesemiconductor memory cell of claim 17, wherein said resistance changeelement comprises a metal-oxide-metal system.
 20. A semiconductor memoryarray, including: a plurality of semiconductor memory cells as recitedin claim 19, arranged in a matrix of rows and columns.